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 $246.54   4.610%   $257.9055   $257.91   $257.90   $257.90  
  Purchase #2 $225.93   8.791%   $245.7915   $245.79   $245.80   $245.80  
  Purchase #3 $192.29   5.345%   $202.5679   $202.57   $202.55   $202.60  
  Purchase #4 $152.99   8.323%   $165.7234   $165.72   $165.70   $165.70  
  Purchase #5 $247.94   9.660%   $271.891   $271.89   $271.90   $271.90  
  Purchase #6 $50.32   9.398%   $55.0491   $55.05   $55.05   $55.00  
  Purchase #7 $10.47   11.287%   $11.6517   $11.65   $11.65   $11.70  
  7 purchase totals = $1,126.48       $1,210.5801   $1,210.58   $1,210.55   $1,210.60