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 $206.75   13.435%   $234.5269   $234.53   $234.55   $234.50  
  Purchase #2 $61.68   11.738%   $68.92   $68.92   $68.90   $68.90  
  Purchase #3 $64.42   8.777%   $70.0741   $70.07   $70.05   $70.10  
  Purchase #4 $202.96   10.279%   $223.8223   $223.82   $223.80   $223.80  
  Purchase #5 $197.93   13.561%   $224.7713   $224.77   $224.75   $224.80  
  Purchase #6 $142.29   6.296%   $151.2486   $151.25   $151.25   $151.20  
  Purchase #7 $201.51   13.790%   $229.2982   $229.30   $229.30   $229.30  
  7 purchase totals = $1,077.54       $1,202.6614   $1,202.66   $1,202.60   $1,202.60