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 $60.41   13.563%   $68.6034   $68.60   $68.60   $68.60  
  Purchase #2 $50.73   10.821%   $56.2195   $56.22   $56.20   $56.20  
  Purchase #3 $130.58   5.511%   $137.7763   $137.78   $137.80   $137.80  
  Purchase #4 $184.57   6.140%   $195.9026   $195.90   $195.90   $195.90  
  Purchase #5 $37.28   11.843%   $41.6951   $41.70   $41.70   $41.70  
  Purchase #6 $125.39   12.688%   $141.2995   $141.30   $141.30   $141.30  
  Purchase #7 $116.26   3.245%   $120.0326   $120.03   $120.05   $120.00  
  7 purchase totals = $705.22       $761.5290   $761.53   $761.55   $761.50