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 $225.75   5.117%   $237.3016   $237.30   $237.30   $237.30  
  Purchase #2 $35.82   10.539%   $39.5951   $39.60   $39.60   $39.60  
  Purchase #3 $58.71   3.319%   $60.6586   $60.66   $60.65   $60.70  
  Purchase #4 $184.40   6.871%   $197.0701   $197.07   $197.05   $197.10  
  Purchase #5 $162.97   3.210%   $168.2013   $168.20   $168.20   $168.20  
  Purchase #6 $94.91   10.737%   $105.1005   $105.10   $105.10   $105.10  
  Purchase #7 $198.50   3.593%   $205.6321   $205.63   $205.65   $205.60  
  7 purchase totals = $961.06       $1,013.5593   $1,013.56   $1,013.55   $1,013.60