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 $228.34   11.563%   $254.743   $254.74   $254.75   $254.70  
  Purchase #2 $127.43   4.681%   $133.395   $133.40   $133.40   $133.40  
  Purchase #3 $211.51   7.438%   $227.2421   $227.24   $227.25   $227.20  
  Purchase #4 $23.51   11.345%   $26.1772   $26.18   $26.20   $26.20  
  Purchase #5 $229.67   13.300%   $260.2161   $260.22   $260.20   $260.20  
  Purchase #6 $42.32   6.132%   $44.9151   $44.92   $44.90   $44.90  
  Purchase #7 $101.56   4.661%   $106.2937   $106.29   $106.30   $106.30  
  7 purchase totals = $964.34       $1,052.9822   $1,052.99   $1,053.00   $1,052.90