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 $82.51   12.296%   $92.6554   $92.66   $92.65   $92.70  
  Purchase #2 $225.62   5.386%   $237.7719   $237.77   $237.75   $237.80  
  Purchase #3 $135.81   3.305%   $140.2985   $140.30   $140.30   $140.30  
  Purchase #4 $212.59   5.611%   $224.5184   $224.52   $224.50   $224.50  
  Purchase #5 $202.79   13.178%   $229.5137   $229.51   $229.50   $229.50  
  Purchase #6 $68.40   9.406%   $74.8337   $74.83   $74.85   $74.80  
  Purchase #7 $14.96   12.286%   $16.798   $16.80   $16.80   $16.80  
  7 purchase totals = $942.68       $1,016.3896   $1,016.39   $1,016.35   $1,016.40