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 $217.74   4.269%   $227.0353   $227.04   $227.05   $227.00  
  Purchase #2 $204.56   10.850%   $226.7548   $226.75   $226.75   $226.80  
  Purchase #3 $168.77   4.690%   $176.6853   $176.69   $176.70   $176.70  
  Purchase #4 $149.64   6.398%   $159.214   $159.21   $159.20   $159.20  
  Purchase #5 $182.65   10.544%   $201.9086   $201.91   $201.90   $201.90  
  Purchase #6 $23.89   13.266%   $27.0592   $27.06   $27.05   $27.10  
  Purchase #7 $44.72   11.453%   $49.8418   $49.84   $49.85   $49.80  
  7 purchase totals = $991.97       $1,068.4990   $1,068.50   $1,068.50   $1,068.50