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 $39.33   13.446%   $44.6183   $44.62   $44.60   $44.60  
  Purchase #2 $65.65   12.700%   $73.9876   $73.99   $74.00   $74.00  
  Purchase #3 $53.98   12.200%   $60.5656   $60.57   $60.55   $60.60  
  Purchase #4 $202.25   6.570%   $215.5378   $215.54   $215.55   $215.50  
  Purchase #5 $57.26   5.792%   $60.5765   $60.58   $60.60   $60.60  
  Purchase #6 $121.60   7.319%   $130.4999   $130.50   $130.50   $130.50  
  Purchase #7 $173.35   3.850%   $180.024   $180.02   $180.00   $180.00  
  7 purchase totals = $713.42       $765.8097   $765.82   $765.80   $765.80