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 $212.26   12.740%   $239.3019   $239.30   $239.30   $239.30  
  Purchase #2 $49.70   10.437%   $54.8872   $54.89   $54.90   $54.90  
  Purchase #3 $245.59   5.108%   $258.1347   $258.13   $258.15   $258.10  
  Purchase #4 $233.36   7.397%   $250.6216   $250.62   $250.60   $250.60  
  Purchase #5 $169.34   3.458%   $175.1958   $175.20   $175.20   $175.20  
  Purchase #6 $85.69   11.822%   $95.8203   $95.82   $95.80   $95.80  
  Purchase #7 $161.68   7.521%   $173.84   $173.84   $173.85   $173.80  
  7 purchase totals = $1,157.62       $1,247.8015   $1,247.80   $1,247.80   $1,247.70