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 $83.27   13.655%   $94.6405   $94.64   $94.65   $94.60  
  Purchase #2 $7.37   5.616%   $7.7839   $7.78   $7.80   $7.80  
  Purchase #3 $133.86   5.696%   $141.4847   $141.48   $141.50   $141.50  
  Purchase #4 $27.49   6.194%   $29.1927   $29.19   $29.20   $29.20  
  Purchase #5 $132.55   12.702%   $149.3865   $149.39   $149.40   $149.40  
  Purchase #6 $59.62   6.404%   $63.4381   $63.44   $63.45   $63.40  
  Purchase #7 $80.37   9.341%   $87.8774   $87.88   $87.90   $87.90  
  7 purchase totals = $524.53       $573.8038   $573.80   $573.90   $573.80