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 $32.98   11.680%   $36.8321   $36.83   $36.85   $36.80  
  Purchase #2 $103.80   9.195%   $113.3444   $113.34   $113.35   $113.30  
  Purchase #3 $225.84   7.481%   $242.7351   $242.74   $242.75   $242.70  
  Purchase #4 $136.99   7.176%   $146.8204   $146.82   $146.80   $146.80  
  Purchase #5 $240.40   6.710%   $256.5308   $256.53   $256.55   $256.50  
  Purchase #6 $20.78   10.402%   $22.9415   $22.94   $22.95   $22.90  
  Purchase #7 $179.61   13.424%   $203.7208   $203.72   $203.70   $203.70  
  7 purchase totals = $940.40       $1,022.9251   $1,022.92   $1,022.95   $1,022.70