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 $94.65   13.595%   $107.5177   $107.52   $107.50   $107.50  
  Purchase #2 $124.82   13.115%   $141.1901   $141.19   $141.20   $141.20  
  Purchase #3 $168.45   7.275%   $180.7047   $180.70   $180.70   $180.70  
  Purchase #4 $184.92   6.821%   $197.5334   $197.53   $197.55   $197.50  
  Purchase #5 $161.43   4.657%   $168.9478   $168.95   $168.95   $168.90  
  Purchase #6 $181.35   6.801%   $193.6836   $193.68   $193.70   $193.70  
  Purchase #7 $46.30   5.286%   $48.7474   $48.75   $48.75   $48.70  
  7 purchase totals = $961.92       $1,038.3247   $1,038.32   $1,038.35   $1,038.20