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 $24.44   5.195%   $25.7097   $25.71   $25.70   $25.70  
  Purchase #2 $136.75   11.833%   $152.9316   $152.93   $152.95   $152.90  
  Purchase #3 $209.38   11.203%   $232.8368   $232.84   $232.85   $232.80  
  Purchase #4 $194.50   12.398%   $218.6141   $218.61   $218.60   $218.60  
  Purchase #5 $144.32   6.499%   $153.6994   $153.70   $153.70   $153.70  
  Purchase #6 $44.99   12.314%   $50.5301   $50.53   $50.55   $50.50  
  Purchase #7 $37.54   10.426%   $41.4539   $41.45   $41.45   $41.50  
  7 purchase totals = $791.92       $875.7756   $875.77   $875.80   $875.70