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 $184.88   9.649%   $202.7191   $202.72   $202.70   $202.70  
  Purchase #2 $111.37   6.516%   $118.6269   $118.63   $118.65   $118.60  
  Purchase #3 $8.31   10.181%   $9.156   $9.16   $9.15   $9.20  
  Purchase #4 $59.85   5.131%   $62.9209   $62.92   $62.90   $62.90  
  Purchase #5 $86.65   9.841%   $95.1772   $95.18   $95.20   $95.20  
  Purchase #6 $46.43   11.618%   $51.8242   $51.82   $51.80   $51.80  
  Purchase #7 $145.98   11.694%   $163.0509   $163.05   $163.05   $163.10  
  7 purchase totals = $643.47       $703.4752   $703.48   $703.45   $703.50