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 $21.58   4.395%   $22.5284   $22.53   $22.55   $22.50  
  Purchase #2 $172.42   8.847%   $187.674   $187.67   $187.65   $187.70  
  Purchase #3 $186.74   9.656%   $204.7716   $204.77   $204.75   $204.80  
  Purchase #4 $6.44   12.663%   $7.2555   $7.26   $7.25   $7.30  
  Purchase #5 $30.79   9.113%   $33.5959   $33.60   $33.60   $33.60  
  Purchase #6 $19.30   7.533%   $20.7539   $20.75   $20.75   $20.80  
  Purchase #7 $204.97   12.121%   $229.8144   $229.81   $229.80   $229.80  
  7 purchase totals = $642.24       $706.3937   $706.39   $706.35   $706.50