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 $192.57   6.235%   $204.5767   $204.58   $204.60   $204.60  
  Purchase #2 $61.70   5.192%   $64.9035   $64.90   $64.90   $64.90  
  Purchase #3 $127.94   9.232%   $139.7514   $139.75   $139.75   $139.80  
  Purchase #4 $207.97   4.560%   $217.4534   $217.45   $217.45   $217.50  
  Purchase #5 $166.71   12.572%   $187.6688   $187.67   $187.65   $187.70  
  Purchase #6 $70.30   3.471%   $72.7401   $72.74   $72.75   $72.70  
  Purchase #7 $159.52   8.594%   $173.2291   $173.23   $173.25   $173.20  
  7 purchase totals = $986.71       $1,060.3230   $1,060.32   $1,060.35   $1,060.40