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 $128.58   3.696%   $133.3323   $133.33   $133.35   $133.30  
  Purchase #2 $66.63   12.560%   $74.9987   $75.00   $75.00   $75.00  
  Purchase #3 $206.77   5.527%   $218.1982   $218.20   $218.20   $218.20  
  Purchase #4 $96.83   5.809%   $102.4549   $102.45   $102.45   $102.50  
  Purchase #5 $104.41   12.597%   $117.5625   $117.56   $117.55   $117.60  
  Purchase #6 $172.77   4.762%   $180.9973   $181.00   $181.00   $181.00  
  Purchase #7 $241.40   5.643%   $255.0222   $255.02   $255.00   $255.00  
  7 purchase totals = $1,017.39       $1,082.5661   $1,082.56   $1,082.55   $1,082.60