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 $44.46   3.257%   $45.9081   $45.91   $45.90   $45.90  
  Purchase #2 $165.57   10.556%   $183.0476   $183.05   $183.05   $183.00  
  Purchase #3 $236.34   8.681%   $256.8567   $256.86   $256.85   $256.90  
  Purchase #4 $155.44   11.856%   $173.869   $173.87   $173.85   $173.90  
  Purchase #5 $245.94   7.703%   $264.8848   $264.88   $264.90   $264.90  
  Purchase #6 $174.98   11.342%   $194.8262   $194.83   $194.85   $194.80  
  Purchase #7 $111.60   7.550%   $120.0258   $120.03   $120.05   $120.00  
  7 purchase totals = $1,134.33       $1,239.4182   $1,239.43   $1,239.45   $1,239.40