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 $91.40   8.636%   $99.2933   $99.29   $99.30   $99.30  
  Purchase #2 $123.44   10.690%   $136.6357   $136.64   $136.65   $136.60  
  Purchase #3 $13.31   6.727%   $14.2054   $14.21   $14.20   $14.20  
  Purchase #4 $235.68   13.457%   $267.3955   $267.40   $267.40   $267.40  
  Purchase #5 $56.28   6.359%   $59.8588   $59.86   $59.85   $59.90  
  Purchase #6 $245.32   5.860%   $259.6958   $259.70   $259.70   $259.70  
  Purchase #7 $190.44   5.520%   $200.9523   $200.95   $200.95   $201.00  
  7 purchase totals = $955.87       $1,038.0368   $1,038.05   $1,038.05   $1,038.10