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 $149.71   11.777%   $167.3413   $167.34   $167.35   $167.30  
  Purchase #2 $199.31   10.156%   $219.5519   $219.55   $219.55   $219.60  
  Purchase #3 $79.87   12.565%   $89.9057   $89.91   $89.90   $89.90  
  Purchase #4 $234.36   12.339%   $263.2777   $263.28   $263.30   $263.30  
  Purchase #5 $133.38   3.363%   $137.8656   $137.87   $137.85   $137.90  
  Purchase #6 $246.91   5.404%   $260.253   $260.25   $260.25   $260.30  
  Purchase #7 $24.79   7.865%   $26.7397   $26.74   $26.75   $26.70  
  7 purchase totals = $1,068.33       $1,164.9349   $1,164.94   $1,164.95   $1,165.00