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 $58.33   6.605%   $62.1827   $62.18   $62.20   $62.20  
  Purchase #2 $64.71   3.146%   $66.7458   $66.75   $66.75   $66.70  
  Purchase #3 $133.81   8.639%   $145.3698   $145.37   $145.35   $145.40  
  Purchase #4 $193.52   5.532%   $204.2255   $204.23   $204.25   $204.20  
  Purchase #5 $73.27   7.845%   $79.018   $79.02   $79.00   $79.00  
  Purchase #6 $35.72   5.200%   $37.5774   $37.58   $37.60   $37.60  
  Purchase #7 $144.39   8.273%   $156.3354   $156.34   $156.35   $156.30  
  7 purchase totals = $703.75       $751.4546   $751.47   $751.50   $751.40