Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $207.33   12.344%   $232.9228   $232.92   $232.90   $232.90  
  Purchase #2 $56.43   6.547%   $60.1245   $60.12   $60.10   $60.10  
  Purchase #3 $135.66   11.654%   $151.4698   $151.47   $151.45   $151.50  
  Purchase #4 $240.67   6.371%   $256.0031   $256.00   $256.00   $256.00  
  Purchase #5 $127.93   10.741%   $141.671   $141.67   $141.65   $141.70  
  Purchase #6 $154.68   13.374%   $175.3669   $175.37   $175.35   $175.40  
  Purchase #7 $152.74   10.739%   $169.1427   $169.14   $169.15   $169.10  
  7 purchase totals = $1,075.44       $1,186.7008   $1,186.69   $1,186.60   $1,186.70