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 $165.83   5.644%   $175.1894   $175.19   $175.20   $175.20  
  Purchase #2 $114.97   5.406%   $121.1853   $121.19   $121.20   $121.20  
  Purchase #3 $238.56   6.689%   $254.5173   $254.52   $254.50   $254.50  
  Purchase #4 $151.57   8.345%   $164.2185   $164.22   $164.20   $164.20  
  Purchase #5 $206.56   6.806%   $220.6185   $220.62   $220.60   $220.60  
  Purchase #6 $142.75   8.316%   $154.6211   $154.62   $154.60   $154.60  
  Purchase #7 $237.94   3.632%   $246.582   $246.58   $246.60   $246.60  
  7 purchase totals = $1,258.18       $1,336.9321   $1,336.94   $1,336.90   $1,336.90