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 $245.43   12.322%   $275.6719   $275.67   $275.65   $275.70  
  Purchase #2 $76.55   8.861%   $83.3331   $83.33   $83.35   $83.30  
  Purchase #3 $105.25   9.714%   $115.474   $115.47   $115.45   $115.50  
  Purchase #4 $72.94   13.753%   $82.9714   $82.97   $82.95   $83.00  
  Purchase #5 $99.67   6.471%   $106.1196   $106.12   $106.10   $106.10  
  Purchase #6 $33.70   6.493%   $35.8881   $35.89   $35.90   $35.90  
  Purchase #7 $225.71   5.364%   $237.8171   $237.82   $237.80   $237.80  
  7 purchase totals = $859.25       $937.2752   $937.27   $937.20   $937.30