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 $82.88   11.862%   $92.7112   $92.71   $92.70   $92.70  
  Purchase #2 $46.57   13.683%   $52.9422   $52.94   $52.95   $52.90  
  Purchase #3 $82.52   5.707%   $87.2294   $87.23   $87.25   $87.20  
  Purchase #4 $228.52   10.108%   $251.6188   $251.62   $251.60   $251.60  
  Purchase #5 $100.98   6.823%   $107.8699   $107.87   $107.85   $107.90  
  Purchase #6 $108.73   4.751%   $113.8958   $113.90   $113.90   $113.90  
  Purchase #7 $223.46   9.208%   $244.0362   $244.04   $244.05   $244.00  
  7 purchase totals = $873.66       $950.3035   $950.31   $950.30   $950.20