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 $140.81   9.481%   $154.1602   $154.16   $154.15   $154.20  
  Purchase #2 $222.27   5.565%   $234.6393   $234.64   $234.65   $234.60  
  Purchase #3 $125.34   8.463%   $135.9475   $135.95   $135.95   $135.90  
  Purchase #4 $235.84   12.282%   $264.8059   $264.81   $264.80   $264.80  
  Purchase #5 $194.71   3.698%   $201.9104   $201.91   $201.90   $201.90  
  Purchase #6 $28.67   12.463%   $32.2431   $32.24   $32.25   $32.20  
  Purchase #7 $57.39   6.773%   $61.277   $61.28   $61.30   $61.30  
  7 purchase totals = $1,005.03       $1,084.9834   $1,084.99   $1,085.00   $1,084.90