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 $55.28   11.184%   $61.4625   $61.46   $61.45   $61.50  
  Purchase #2 $214.54   13.273%   $243.0159   $243.02   $243.00   $243.00  
  Purchase #3 $243.58   5.113%   $256.0342   $256.03   $256.05   $256.00  
  Purchase #4 $238.37   4.696%   $249.5639   $249.56   $249.55   $249.60  
  Purchase #5 $17.73   5.351%   $18.6787   $18.68   $18.70   $18.70  
  Purchase #6 $183.89   11.341%   $204.745   $204.75   $204.75   $204.70  
  Purchase #7 $193.42   9.232%   $211.2765   $211.28   $211.30   $211.30  
  7 purchase totals = $1,146.81       $1,244.7767   $1,244.78   $1,244.80   $1,244.80