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 $207.79   4.264%   $216.6502   $216.65   $216.65   $216.70  
  Purchase #2 $88.36   9.874%   $97.0847   $97.08   $97.10   $97.10  
  Purchase #3 $38.66   13.782%   $43.9881   $43.99   $44.00   $44.00  
  Purchase #4 $118.30   11.102%   $131.4337   $131.43   $131.45   $131.40  
  Purchase #5 $56.45   7.171%   $60.498   $60.50   $60.50   $60.50  
  Purchase #6 $96.77   5.195%   $101.7972   $101.80   $101.80   $101.80  
  Purchase #7 $199.32   3.864%   $207.0217   $207.02   $207.00   $207.00  
  7 purchase totals = $805.65       $858.4736   $858.47   $858.50   $858.50