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 $136.53   13.167%   $154.5069   $154.51   $154.50   $154.50  
  Purchase #2 $235.33   10.202%   $259.3384   $259.34   $259.35   $259.30  
  Purchase #3 $161.31   8.167%   $174.4842   $174.48   $174.50   $174.50  
  Purchase #4 $209.87   4.508%   $219.3309   $219.33   $219.35   $219.30  
  Purchase #5 $56.92   10.201%   $62.7264   $62.73   $62.75   $62.70  
  Purchase #6 $95.87   7.167%   $102.741   $102.74   $102.75   $102.70  
  Purchase #7 $127.25   6.521%   $135.548   $135.55   $135.55   $135.50  
  7 purchase totals = $1,023.08       $1,108.6758   $1,108.68   $1,108.75   $1,108.50