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 $114.61   10.674%   $126.8435   $126.84   $126.85   $126.80  
  Purchase #2 $8.27   9.816%   $9.0818   $9.08   $9.10   $9.10  
  Purchase #3 $165.52   6.800%   $176.7754   $176.78   $176.80   $176.80  
  Purchase #4 $196.36   7.289%   $210.6727   $210.67   $210.65   $210.70  
  Purchase #5 $245.39   12.331%   $275.649   $275.65   $275.65   $275.60  
  Purchase #6 $82.93   12.544%   $93.3327   $93.33   $93.35   $93.30  
  Purchase #7 $102.55   8.664%   $111.4349   $111.43   $111.45   $111.40  
  7 purchase totals = $915.63       $1,003.7900   $1,003.78   $1,003.85   $1,003.70