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 $54.76   5.842%   $57.9591   $57.96   $57.95   $58.00  
  Purchase #2 $32.42   12.598%   $36.5043   $36.50   $36.50   $36.50  
  Purchase #3 $46.34   5.776%   $49.0166   $49.02   $49.00   $49.00  
  Purchase #4 $110.43   5.435%   $116.4319   $116.43   $116.45   $116.40  
  Purchase #5 $57.58   5.303%   $60.6335   $60.63   $60.65   $60.60  
  Purchase #6 $75.67   6.774%   $80.7959   $80.80   $80.80   $80.80  
  Purchase #7 $225.81   3.738%   $234.2508   $234.25   $234.25   $234.30  
  7 purchase totals = $603.01       $635.5921   $635.59   $635.60   $635.60