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 $177.67   8.591%   $192.9336   $192.93   $192.95   $192.90  
  Purchase #2 $87.97   8.216%   $95.1976   $95.20   $95.20   $95.20  
  Purchase #3 $193.42   9.737%   $212.2533   $212.25   $212.25   $212.30  
  Purchase #4 $238.54   7.181%   $255.6696   $255.67   $255.65   $255.70  
  Purchase #5 $62.28   6.647%   $66.4198   $66.42   $66.40   $66.40  
  Purchase #6 $104.56   3.762%   $108.4935   $108.49   $108.50   $108.50  
  Purchase #7 $225.42   13.451%   $255.7412   $255.74   $255.75   $255.70  
  7 purchase totals = $1,089.86       $1,186.7086   $1,186.70   $1,186.70   $1,186.70