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 $62.97   3.251%   $65.0172   $65.02   $65.00   $65.00  
  Purchase #2 $244.57   7.145%   $262.0445   $262.04   $262.05   $262.00  
  Purchase #3 $82.45   10.252%   $90.9028   $90.90   $90.90   $90.90  
  Purchase #4 $20.74   9.586%   $22.7281   $22.73   $22.75   $22.70  
  Purchase #5 $128.93   3.472%   $133.4064   $133.41   $133.40   $133.40  
  Purchase #6 $47.31   12.504%   $53.2256   $53.23   $53.25   $53.20  
  Purchase #7 $19.84   13.647%   $22.5476   $22.55   $22.55   $22.50  
  7 purchase totals = $606.81       $649.8722   $649.88   $649.90   $649.70