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 $85.48   11.737%   $95.5128   $95.51   $95.50   $95.50  
  Purchase #2 $6.38   6.813%   $6.8147   $6.81   $6.80   $6.80  
  Purchase #3 $132.39   12.844%   $149.3942   $149.39   $149.40   $149.40  
  Purchase #4 $131.60   3.731%   $136.51   $136.51   $136.50   $136.50  
  Purchase #5 $179.38   6.667%   $191.3393   $191.34   $191.35   $191.30  
  Purchase #6 $225.32   4.322%   $235.0583   $235.06   $235.05   $235.10  
  Purchase #7 $195.57   8.190%   $211.5872   $211.59   $211.60   $211.60  
  7 purchase totals = $956.12       $1,026.2165   $1,026.21   $1,026.20   $1,026.20