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 $171.60   11.516%   $191.3615   $191.36   $191.35   $191.40  
  Purchase #2 $201.43   11.751%   $225.1   $225.10   $225.10   $225.10  
  Purchase #3 $40.57   13.186%   $45.9196   $45.92   $45.90   $45.90  
  Purchase #4 $93.95   10.420%   $103.7396   $103.74   $103.75   $103.70  
  Purchase #5 $163.83   7.219%   $175.6569   $175.66   $175.65   $175.70  
  Purchase #6 $175.45   4.294%   $182.9838   $182.98   $183.00   $183.00  
  Purchase #7 $64.80   4.113%   $67.4652   $67.47   $67.45   $67.50  
  7 purchase totals = $911.63       $992.2266   $992.23   $992.20   $992.30