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 $166.94   5.141%   $175.5224   $175.52   $175.50   $175.50  
  Purchase #2 $210.98   7.411%   $226.6157   $226.62   $226.60   $226.60  
  Purchase #3 $222.25   9.140%   $242.5637   $242.56   $242.55   $242.60  
  Purchase #4 $29.44   8.404%   $31.9141   $31.91   $31.90   $31.90  
  Purchase #5 $28.26   3.648%   $29.2909   $29.29   $29.30   $29.30  
  Purchase #6 $10.34   3.491%   $10.701   $10.70   $10.70   $10.70  
  Purchase #7 $120.28   3.274%   $124.218   $124.22   $124.20   $124.20  
  7 purchase totals = $788.49       $840.8258   $840.82   $840.75   $840.80