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 $31.46   11.253%   $35.0002   $35.00   $35.00   $35.00  
  Purchase #2 $243.78   5.807%   $257.9363   $257.94   $257.95   $257.90  
  Purchase #3 $196.53   10.140%   $216.4581   $216.46   $216.45   $216.50  
  Purchase #4 $154.31   7.155%   $165.3509   $165.35   $165.35   $165.40  
  Purchase #5 $123.80   9.785%   $135.9138   $135.91   $135.90   $135.90  
  Purchase #6 $133.38   6.464%   $142.0017   $142.00   $142.00   $142.00  
  Purchase #7 $72.75   9.522%   $79.6773   $79.68   $79.70   $79.70  
  7 purchase totals = $956.01       $1,032.3383   $1,032.34   $1,032.35   $1,032.40