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 $248.89   6.843%   $265.9215   $265.92   $265.90   $265.90  
  Purchase #2 $211.70   13.833%   $240.9845   $240.98   $241.00   $241.00  
  Purchase #3 $86.82   6.812%   $92.7342   $92.73   $92.75   $92.70  
  Purchase #4 $229.54   12.205%   $257.5554   $257.56   $257.55   $257.60  
  Purchase #5 $160.93   5.708%   $170.1159   $170.12   $170.10   $170.10  
  Purchase #6 $181.48   3.290%   $187.4507   $187.45   $187.45   $187.50  
  Purchase #7 $7.44   5.329%   $7.8365   $7.84   $7.85   $7.80  
  7 purchase totals = $1,126.80       $1,222.5987   $1,222.60   $1,222.60   $1,222.60