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 $227.49   8.651%   $247.1702   $247.17   $247.15   $247.20  
  Purchase #2 $163.71   6.726%   $174.7211   $174.72   $174.70   $174.70  
  Purchase #3 $161.95   8.552%   $175.8   $175.80   $175.80   $175.80  
  Purchase #4 $8.89   9.625%   $9.7457   $9.75   $9.75   $9.70  
  Purchase #5 $231.35   11.392%   $257.7054   $257.71   $257.70   $257.70  
  Purchase #6 $169.53   8.329%   $183.6502   $183.65   $183.65   $183.70  
  Purchase #7 $95.25   9.793%   $104.5778   $104.58   $104.60   $104.60  
  7 purchase totals = $1,058.17       $1,153.3704   $1,153.38   $1,153.35   $1,153.40