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 $90.36   5.384%   $95.225   $95.23   $95.25   $95.20  
  Purchase #2 $101.95   10.702%   $112.8607   $112.86   $112.85   $112.90  
  Purchase #3 $77.75   11.452%   $86.6539   $86.65   $86.65   $86.70  
  Purchase #4 $225.56   8.313%   $244.3108   $244.31   $244.30   $244.30  
  Purchase #5 $136.25   5.655%   $143.9549   $143.95   $143.95   $144.00  
  Purchase #6 $211.50   8.254%   $228.9572   $228.96   $228.95   $229.00  
  Purchase #7 $11.30   9.436%   $12.3663   $12.37   $12.35   $12.40  
  7 purchase totals = $854.67       $924.3288   $924.33   $924.30   $924.50