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 $25.49   4.808%   $26.7156   $26.72   $26.70   $26.70  
  Purchase #2 $119.84   3.455%   $123.9805   $123.98   $124.00   $124.00  
  Purchase #3 $194.93   7.815%   $210.1638   $210.16   $210.15   $210.20  
  Purchase #4 $239.80   7.107%   $256.8426   $256.84   $256.85   $256.80  
  Purchase #5 $33.26   8.543%   $36.1014   $36.10   $36.10   $36.10  
  Purchase #6 $141.72   11.704%   $158.3069   $158.31   $158.30   $158.30  
  Purchase #7 $212.73   6.294%   $226.1192   $226.12   $226.10   $226.10  
  7 purchase totals = $967.77       $1,038.2300   $1,038.23   $1,038.20   $1,038.20