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 $247.53   8.286%   $268.0403   $268.04   $268.05   $268.00  
  Purchase #2 $43.47   12.681%   $48.9824   $48.98   $49.00   $49.00  
  Purchase #3 $214.53   6.703%   $228.9099   $228.91   $228.90   $228.90  
  Purchase #4 $77.92   13.738%   $88.6246   $88.62   $88.60   $88.60  
  Purchase #5 $54.67   8.714%   $59.4339   $59.43   $59.45   $59.40  
  Purchase #6 $238.28   5.858%   $252.2384   $252.24   $252.25   $252.20  
  Purchase #7 $101.67   4.363%   $106.1059   $106.11   $106.10   $106.10  
  7 purchase totals = $978.07       $1,052.3354   $1,052.33   $1,052.35   $1,052.20