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 $108.61   7.518%   $116.7753   $116.78   $116.80   $116.80  
  Purchase #2 $91.99   11.108%   $102.2082   $102.21   $102.20   $102.20  
  Purchase #3 $152.29   13.725%   $173.1918   $173.19   $173.20   $173.20  
  Purchase #4 $246.84   8.623%   $268.125   $268.13   $268.15   $268.10  
  Purchase #5 $217.90   13.668%   $247.6826   $247.68   $247.70   $247.70  
  Purchase #6 $47.71   8.437%   $51.7353   $51.74   $51.75   $51.70  
  Purchase #7 $127.67   12.411%   $143.5151   $143.52   $143.50   $143.50  
  7 purchase totals = $993.01       $1,103.2333   $1,103.25   $1,103.30   $1,103.20