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 $97.61   13.869%   $111.1475   $111.15   $111.15   $111.10  
  Purchase #2 $59.93   4.671%   $62.7293   $62.73   $62.75   $62.70  
  Purchase #3 $197.41   12.319%   $221.7289   $221.73   $221.75   $221.70  
  Purchase #4 $241.35   12.695%   $271.9894   $271.99   $272.00   $272.00  
  Purchase #5 $52.35   6.137%   $55.5627   $55.56   $55.55   $55.60  
  Purchase #6 $235.80   3.498%   $244.0483   $244.05   $244.05   $244.00  
  Purchase #7 $59.62   5.767%   $63.0583   $63.06   $63.05   $63.10  
  7 purchase totals = $944.07       $1,030.2644   $1,030.27   $1,030.30   $1,030.20