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 $221.35   5.242%   $232.9532   $232.95   $232.95   $233.00  
  Purchase #2 $95.93   10.146%   $105.6631   $105.66   $105.65   $105.70  
  Purchase #3 $206.94   5.235%   $217.7733   $217.77   $217.75   $217.80  
  Purchase #4 $43.56   12.780%   $49.127   $49.13   $49.15   $49.10  
  Purchase #5 $175.29   10.789%   $194.202   $194.20   $194.20   $194.20  
  Purchase #6 $86.79   3.841%   $90.1236   $90.12   $90.10   $90.10  
  Purchase #7 $63.43   12.604%   $71.4247   $71.42   $71.40   $71.40  
  7 purchase totals = $893.29       $961.2669   $961.25   $961.20   $961.30