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 $38.92   13.739%   $44.2672   $44.27   $44.25   $44.30  
  Purchase #2 $91.26   11.118%   $101.4063   $101.41   $101.40   $101.40  
  Purchase #3 $225.67   11.233%   $251.0195   $251.02   $251.00   $251.00  
  Purchase #4 $132.46   9.167%   $144.6026   $144.60   $144.60   $144.60  
  Purchase #5 $155.51   6.507%   $165.629   $165.63   $165.65   $165.60  
  Purchase #6 $193.93   13.566%   $220.2385   $220.24   $220.25   $220.20  
  Purchase #7 $117.34   9.415%   $128.3876   $128.39   $128.40   $128.40  
  7 purchase totals = $955.09       $1,055.5507   $1,055.56   $1,055.55   $1,055.50