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 $190.33   7.719%   $205.0216   $205.02   $205.00   $205.00  
  Purchase #2 $189.57   4.294%   $197.7101   $197.71   $197.70   $197.70  
  Purchase #3 $140.62   8.869%   $153.0916   $153.09   $153.10   $153.10  
  Purchase #4 $133.84   13.631%   $152.0837   $152.08   $152.10   $152.10  
  Purchase #5 $209.83   9.594%   $229.9611   $229.96   $229.95   $230.00  
  Purchase #6 $85.51   11.771%   $95.5754   $95.58   $95.60   $95.60  
  Purchase #7 $209.41   13.132%   $236.9097   $236.91   $236.90   $236.90  
  7 purchase totals = $1,159.11       $1,270.3532   $1,270.35   $1,270.35   $1,270.40