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 $120.41   10.416%   $132.9519   $132.95   $132.95   $133.00  
  Purchase #2 $190.67   3.295%   $196.9526   $196.95   $196.95   $197.00  
  Purchase #3 $173.46   6.183%   $184.185   $184.19   $184.20   $184.20  
  Purchase #4 $29.50   8.341%   $31.9606   $31.96   $31.95   $32.00  
  Purchase #5 $64.74   5.561%   $68.3402   $68.34   $68.35   $68.30  
  Purchase #6 $73.33   5.767%   $77.5589   $77.56   $77.55   $77.60  
  Purchase #7 $125.48   5.479%   $132.355   $132.36   $132.35   $132.40  
  7 purchase totals = $777.59       $824.3042   $824.31   $824.30   $824.50