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 $238.59   3.759%   $247.5586   $247.56   $247.55   $247.60  
  Purchase #2 $229.80   5.853%   $243.2502   $243.25   $243.25   $243.30  
  Purchase #3 $204.98   5.182%   $215.6021   $215.60   $215.60   $215.60  
  Purchase #4 $229.96   6.449%   $244.7901   $244.79   $244.80   $244.80  
  Purchase #5 $63.75   6.534%   $67.9154   $67.92   $67.90   $67.90  
  Purchase #6 $152.94   11.672%   $170.7912   $170.79   $170.80   $170.80  
  Purchase #7 $56.97   11.399%   $63.464   $63.46   $63.45   $63.50  
  7 purchase totals = $1,176.99       $1,253.3716   $1,253.37   $1,253.35   $1,253.50