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 $84.64   8.872%   $92.1493   $92.15   $92.15   $92.10  
  Purchase #2 $175.68   11.701%   $196.2363   $196.24   $196.25   $196.20  
  Purchase #3 $39.52   4.767%   $41.4039   $41.40   $41.40   $41.40  
  Purchase #4 $58.55   10.108%   $64.4682   $64.47   $64.45   $64.50  
  Purchase #5 $148.73   9.791%   $163.2922   $163.29   $163.30   $163.30  
  Purchase #6 $161.28   3.237%   $166.5006   $166.50   $166.50   $166.50  
  Purchase #7 $59.70   5.447%   $62.9519   $62.95   $62.95   $63.00  
  7 purchase totals = $728.10       $787.0024   $787.00   $787.00   $787.00