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 $60.61   4.822%   $63.5326   $63.53   $63.55   $63.50  
  Purchase #2 $203.98   7.417%   $219.1092   $219.11   $219.10   $219.10  
  Purchase #3 $244.65   13.472%   $277.6092   $277.61   $277.60   $277.60  
  Purchase #4 $125.62   5.581%   $132.6309   $132.63   $132.65   $132.60  
  Purchase #5 $18.98   8.517%   $20.5965   $20.60   $20.60   $20.60  
  Purchase #6 $45.89   11.575%   $51.2018   $51.20   $51.20   $51.20  
  Purchase #7 $120.29   7.156%   $128.898   $128.90   $128.90   $128.90  
  7 purchase totals = $820.02       $893.5782   $893.58   $893.60   $893.50