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 $83.87   12.788%   $94.5953   $94.60   $94.60   $94.60  
  Purchase #2 $222.92   11.631%   $248.8478   $248.85   $248.85   $248.80  
  Purchase #3 $167.25   5.668%   $176.7297   $176.73   $176.75   $176.70  
  Purchase #4 $62.43   9.465%   $68.339   $68.34   $68.35   $68.30  
  Purchase #5 $108.57   8.569%   $117.8734   $117.87   $117.85   $117.90  
  Purchase #6 $52.60   3.161%   $54.2627   $54.26   $54.25   $54.30  
  Purchase #7 $44.31   3.582%   $45.8972   $45.90   $45.90   $45.90  
  7 purchase totals = $741.95       $806.5451   $806.55   $806.55   $806.50