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 $102.86   13.355%   $116.597   $116.60   $116.60   $116.60  
  Purchase #2 $75.28   12.402%   $84.6162   $84.62   $84.60   $84.60  
  Purchase #3 $150.68   11.288%   $167.6888   $167.69   $167.70   $167.70  
  Purchase #4 $181.88   5.668%   $192.189   $192.19   $192.20   $192.20  
  Purchase #5 $242.79   10.666%   $268.686   $268.69   $268.70   $268.70  
  Purchase #6 $61.34   5.212%   $64.537   $64.54   $64.55   $64.50  
  Purchase #7 $200.73   12.516%   $225.8534   $225.85   $225.85   $225.90  
  7 purchase totals = $1,015.56       $1,120.1674   $1,120.18   $1,120.20   $1,120.20