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 $50.45   5.654%   $53.3024   $53.30   $53.30   $53.30  
  Purchase #2 $136.94   13.620%   $155.5912   $155.59   $155.60   $155.60  
  Purchase #3 $189.58   5.331%   $199.6865   $199.69   $199.70   $199.70  
  Purchase #4 $214.82   10.107%   $236.5319   $236.53   $236.55   $236.50  
  Purchase #5 $216.80   13.260%   $245.5477   $245.55   $245.55   $245.50  
  Purchase #6 $141.43   7.216%   $151.6356   $151.64   $151.65   $151.60  
  Purchase #7 $202.49   11.453%   $225.6812   $225.68   $225.70   $225.70  
  7 purchase totals = $1,152.51       $1,267.9765   $1,267.98   $1,268.05   $1,267.90