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 $39.85   11.606%   $44.475   $44.48   $44.50   $44.50  
  Purchase #2 $200.47   11.658%   $223.8408   $223.84   $223.85   $223.80  
  Purchase #3 $245.94   3.500%   $254.5479   $254.55   $254.55   $254.50  
  Purchase #4 $250.29   10.353%   $276.2025   $276.20   $276.20   $276.20  
  Purchase #5 $247.52   13.772%   $281.6085   $281.61   $281.60   $281.60  
  Purchase #6 $233.74   3.783%   $242.5824   $242.58   $242.60   $242.60  
  Purchase #7 $142.42   11.363%   $158.6032   $158.60   $158.60   $158.60  
  7 purchase totals = $1,360.23       $1,481.8603   $1,481.86   $1,481.90   $1,481.80