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 $87.39   9.772%   $95.9298   $95.93   $95.95   $95.90  
  Purchase #2 $5.96   6.248%   $6.3324   $6.33   $6.35   $6.30  
  Purchase #3 $225.49   3.683%   $233.7948   $233.79   $233.80   $233.80  
  Purchase #4 $58.35   3.831%   $60.5854   $60.59   $60.60   $60.60  
  Purchase #5 $100.44   10.569%   $111.0555   $111.06   $111.05   $111.10  
  Purchase #6 $219.97   8.859%   $239.4571   $239.46   $239.45   $239.50  
  Purchase #7 $62.87   8.426%   $68.1674   $68.17   $68.15   $68.20  
  7 purchase totals = $760.47       $815.3224   $815.33   $815.35   $815.40