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 $167.67   10.776%   $185.7381   $185.74   $185.75   $185.70  
  Purchase #2 $154.65   12.726%   $174.3308   $174.33   $174.35   $174.30  
  Purchase #3 $225.73   11.416%   $251.4993   $251.50   $251.50   $251.50  
  Purchase #4 $78.77   13.416%   $89.3378   $89.34   $89.35   $89.30  
  Purchase #5 $217.47   8.208%   $235.3199   $235.32   $235.30   $235.30  
  Purchase #6 $58.91   5.773%   $62.3109   $62.31   $62.30   $62.30  
  Purchase #7 $22.46   13.197%   $25.424   $25.42   $25.40   $25.40  
  7 purchase totals = $925.66       $1,023.9608   $1,023.96   $1,023.95   $1,023.80