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 $44.72   13.524%   $50.7679   $50.77   $50.75   $50.80  
  Purchase #2 $192.91   8.630%   $209.5581   $209.56   $209.55   $209.60  
  Purchase #3 $96.29   9.263%   $105.2093   $105.21   $105.20   $105.20  
  Purchase #4 $183.54   4.220%   $191.2854   $191.29   $191.30   $191.30  
  Purchase #5 $162.78   8.807%   $177.116   $177.12   $177.10   $177.10  
  Purchase #6 $58.37   9.855%   $64.1224   $64.12   $64.10   $64.10  
  Purchase #7 $234.93   3.824%   $243.9137   $243.91   $243.90   $243.90  
  7 purchase totals = $973.54       $1,041.9728   $1,041.98   $1,041.90   $1,042.00