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 $211.61   13.534%   $240.2493   $240.25   $240.25   $240.20  
  Purchase #2 $202.56   12.201%   $227.2743   $227.27   $227.25   $227.30  
  Purchase #3 $250.40   6.674%   $267.1117   $267.11   $267.10   $267.10  
  Purchase #4 $189.28   6.235%   $201.0816   $201.08   $201.10   $201.10  
  Purchase #5 $17.59   3.718%   $18.244   $18.24   $18.25   $18.20  
  Purchase #6 $218.64   12.259%   $245.4431   $245.44   $245.45   $245.40  
  Purchase #7 $133.64   12.207%   $149.9534   $149.95   $149.95   $150.00  
  7 purchase totals = $1,223.72       $1,349.3574   $1,349.34   $1,349.35   $1,349.30