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 $233.27   5.858%   $246.935   $246.94   $246.95   $246.90  
  Purchase #2 $103.68   8.794%   $112.7976   $112.80   $112.80   $112.80  
  Purchase #3 $119.58   8.478%   $129.718   $129.72   $129.70   $129.70  
  Purchase #4 $191.33   4.798%   $200.51   $200.51   $200.50   $200.50  
  Purchase #5 $94.33   11.191%   $104.8865   $104.89   $104.90   $104.90  
  Purchase #6 $110.51   6.673%   $117.8843   $117.88   $117.90   $117.90  
  Purchase #7 $127.75   8.748%   $138.9256   $138.93   $138.95   $138.90  
  7 purchase totals = $980.45       $1,051.6570   $1,051.67   $1,051.70   $1,051.60