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 $58.48   12.826%   $65.9806   $65.98   $66.00   $66.00  
  Purchase #2 $69.93   8.204%   $75.6671   $75.67   $75.65   $75.70  
  Purchase #3 $20.61   12.432%   $23.1722   $23.17   $23.15   $23.20  
  Purchase #4 $212.73   5.829%   $225.13   $225.13   $225.15   $225.10  
  Purchase #5 $47.48   4.331%   $49.5364   $49.54   $49.55   $49.50  
  Purchase #6 $131.94   7.610%   $141.9806   $141.98   $142.00   $142.00  
  Purchase #7 $105.55   12.407%   $118.6456   $118.65   $118.65   $118.60  
  7 purchase totals = $646.72       $700.1125   $700.12   $700.15   $700.10