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 $173.69   11.805%   $194.1941   $194.19   $194.20   $194.20  
  Purchase #2 $57.26   6.456%   $60.9567   $60.96   $60.95   $61.00  
  Purchase #3 $178.90   10.614%   $197.8884   $197.89   $197.90   $197.90  
  Purchase #4 $232.43   3.679%   $240.9811   $240.98   $241.00   $241.00  
  Purchase #5 $229.60   3.819%   $238.3684   $238.37   $238.35   $238.40  
  Purchase #6 $170.55   3.684%   $176.8331   $176.83   $176.85   $176.80  
  Purchase #7 $119.45   13.807%   $135.9425   $135.94   $135.95   $135.90  
  7 purchase totals = $1,161.88       $1,245.1643   $1,245.16   $1,245.20   $1,245.20