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 $58.34   6.116%   $61.9081   $61.91   $61.90   $61.90  
  Purchase #2 $133.79   12.449%   $150.4455   $150.45   $150.45   $150.40  
  Purchase #3 $235.78   11.549%   $263.0102   $263.01   $263.00   $263.00  
  Purchase #4 $149.50   12.727%   $168.5269   $168.53   $168.55   $168.50  
  Purchase #5 $191.52   5.124%   $201.3335   $201.33   $201.35   $201.30  
  Purchase #6 $210.40   12.738%   $237.2008   $237.20   $237.20   $237.20  
  Purchase #7 $149.29   5.655%   $157.7323   $157.73   $157.75   $157.70  
  7 purchase totals = $1,128.62       $1,240.1573   $1,240.16   $1,240.20   $1,240.00