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 $92.74   6.188%   $98.4788   $98.48   $98.50   $98.50  
  Purchase #2 $57.37   3.766%   $59.5306   $59.53   $59.55   $59.50  
  Purchase #3 $63.36   7.536%   $68.1348   $68.13   $68.15   $68.10  
  Purchase #4 $226.37   6.782%   $241.7224   $241.72   $241.70   $241.70  
  Purchase #5 $210.40   9.297%   $229.9609   $229.96   $229.95   $230.00  
  Purchase #6 $235.57   12.711%   $265.5133   $265.51   $265.50   $265.50  
  Purchase #7 $111.50   12.227%   $125.1331   $125.13   $125.15   $125.10  
  7 purchase totals = $997.31       $1,088.4739   $1,088.46   $1,088.50   $1,088.40