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 $56.51   7.178%   $60.5663   $60.57   $60.55   $60.60  
  Purchase #2 $122.33   8.870%   $133.1807   $133.18   $133.20   $133.20  
  Purchase #3 $158.83   4.213%   $165.5215   $165.52   $165.50   $165.50  
  Purchase #4 $246.39   9.563%   $269.9523   $269.95   $269.95   $270.00  
  Purchase #5 $41.98   13.390%   $47.6011   $47.60   $47.60   $47.60  
  Purchase #6 $30.62   8.424%   $33.1994   $33.20   $33.20   $33.20  
  Purchase #7 $45.37   5.679%   $47.9466   $47.95   $47.95   $47.90  
  7 purchase totals = $702.03       $757.9679   $757.97   $757.95   $758.00