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 $46.38   11.203%   $51.576   $51.58   $51.60   $51.60  
  Purchase #2 $93.31   12.349%   $104.8329   $104.83   $104.85   $104.80  
  Purchase #3 $245.33   5.710%   $259.3383   $259.34   $259.35   $259.30  
  Purchase #4 $176.42   8.333%   $191.1211   $191.12   $191.10   $191.10  
  Purchase #5 $32.96   4.783%   $34.5365   $34.54   $34.55   $34.50  
  Purchase #6 $167.27   5.227%   $176.0132   $176.01   $176.00   $176.00  
  Purchase #7 $196.42   4.385%   $205.033   $205.03   $205.05   $205.00  
  7 purchase totals = $958.09       $1,022.4510   $1,022.45   $1,022.50   $1,022.30