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 $246.56   12.591%   $277.6044   $277.60   $277.60   $277.60  
  Purchase #2 $203.88   11.204%   $226.7227   $226.72   $226.70   $226.70  
  Purchase #3 $218.94   12.434%   $246.163   $246.16   $246.15   $246.20  
  Purchase #4 $200.34   10.592%   $221.56   $221.56   $221.55   $221.60  
  Purchase #5 $87.66   8.145%   $94.7999   $94.80   $94.80   $94.80  
  Purchase #6 $178.94   7.331%   $192.0581   $192.06   $192.05   $192.10  
  Purchase #7 $115.41   7.742%   $124.345   $124.35   $124.35   $124.30  
  7 purchase totals = $1,251.73       $1,383.2531   $1,383.25   $1,383.20   $1,383.30