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 $60.79   9.729%   $66.7043   $66.70   $66.70   $66.70  
  Purchase #2 $164.91   10.282%   $181.866   $181.87   $181.85   $181.90  
  Purchase #3 $78.70   11.398%   $87.6702   $87.67   $87.65   $87.70  
  Purchase #4 $188.69   9.169%   $205.991   $205.99   $206.00   $206.00  
  Purchase #5 $44.47   9.824%   $48.8387   $48.84   $48.85   $48.80  
  Purchase #6 $53.37   5.224%   $56.158   $56.16   $56.15   $56.20  
  Purchase #7 $139.43   12.366%   $156.6719   $156.67   $156.65   $156.70  
  7 purchase totals = $730.36       $803.9001   $803.90   $803.85   $804.00