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 $60.52   4.281%   $63.1109   $63.11   $63.10   $63.10  
  Purchase #2 $229.92   5.561%   $242.7059   $242.71   $242.70   $242.70  
  Purchase #3 $113.82   3.496%   $117.7991   $117.80   $117.80   $117.80  
  Purchase #4 $191.58   11.111%   $212.8665   $212.87   $212.85   $212.90  
  Purchase #5 $175.43   8.431%   $190.2205   $190.22   $190.20   $190.20  
  Purchase #6 $36.26   4.755%   $37.9842   $37.98   $38.00   $38.00  
  Purchase #7 $69.55   5.749%   $73.5484   $73.55   $73.55   $73.50  
  7 purchase totals = $877.08       $938.2355   $938.24   $938.20   $938.20