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 $104.46   4.270%   $108.9204   $108.92   $108.90   $108.90  
  Purchase #2 $176.29   10.821%   $195.3663   $195.37   $195.35   $195.40  
  Purchase #3 $177.73   6.117%   $188.6017   $188.60   $188.60   $188.60  
  Purchase #4 $155.94   9.568%   $170.8603   $170.86   $170.85   $170.90  
  Purchase #5 $207.66   9.235%   $226.8374   $226.84   $226.85   $226.80  
  Purchase #6 $35.34   11.626%   $39.4486   $39.45   $39.45   $39.40  
  Purchase #7 $73.82   9.218%   $80.6247   $80.62   $80.60   $80.60  
  7 purchase totals = $931.24       $1,010.6594   $1,010.66   $1,010.60   $1,010.60