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 $246.73   11.564%   $275.2619   $275.26   $275.25   $275.30  
  Purchase #2 $105.40   12.261%   $118.3231   $118.32   $118.30   $118.30  
  Purchase #3 $80.54   9.174%   $87.9287   $87.93   $87.95   $87.90  
  Purchase #4 $95.81   13.318%   $108.57   $108.57   $108.55   $108.60  
  Purchase #5 $243.47   3.286%   $251.4704   $251.47   $251.45   $251.50  
  Purchase #6 $91.92   6.199%   $97.6181   $97.62   $97.60   $97.60  
  Purchase #7 $12.78   8.300%   $13.8407   $13.84   $13.85   $13.80  
  7 purchase totals = $876.65       $953.0129   $953.01   $952.95   $953.00