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 $203.38   8.511%   $220.6897   $220.69   $220.70   $220.70  
  Purchase #2 $119.25   7.441%   $128.1234   $128.12   $128.10   $128.10  
  Purchase #3 $216.36   5.336%   $227.905   $227.91   $227.90   $227.90  
  Purchase #4 $49.63   9.597%   $54.393   $54.39   $54.40   $54.40  
  Purchase #5 $194.55   12.415%   $218.7034   $218.70   $218.70   $218.70  
  Purchase #6 $143.80   7.676%   $154.8381   $154.84   $154.85   $154.80  
  Purchase #7 $71.31   9.319%   $77.9554   $77.96   $77.95   $78.00  
  7 purchase totals = $998.28       $1,082.6080   $1,082.61   $1,082.60   $1,082.60