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 $201.97   12.559%   $227.3354   $227.34   $227.35   $227.30  
  Purchase #2 $139.68   8.703%   $151.8364   $151.84   $151.85   $151.80  
  Purchase #3 $60.65   11.782%   $67.7958   $67.80   $67.80   $67.80  
  Purchase #4 $36.79   8.364%   $39.8671   $39.87   $39.85   $39.90  
  Purchase #5 $142.52   6.809%   $152.2242   $152.22   $152.20   $152.20  
  Purchase #6 $20.33   5.784%   $21.5059   $21.51   $21.50   $21.50  
  Purchase #7 $227.87   3.484%   $235.809   $235.81   $235.80   $235.80  
  7 purchase totals = $829.81       $896.3738   $896.39   $896.35   $896.30