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 $241.83   4.650%   $253.0751   $253.08   $253.10   $253.10  
  Purchase #2 $171.78   9.177%   $187.5443   $187.54   $187.55   $187.50  
  Purchase #3 $16.58   8.465%   $17.9835   $17.98   $18.00   $18.00  
  Purchase #4 $134.80   10.582%   $149.0645   $149.06   $149.05   $149.10  
  Purchase #5 $142.60   9.224%   $155.7534   $155.75   $155.75   $155.80  
  Purchase #6 $189.82   7.783%   $204.5937   $204.59   $204.60   $204.60  
  Purchase #7 $84.70   10.425%   $93.53   $93.53   $93.55   $93.50  
  7 purchase totals = $982.11       $1,061.5445   $1,061.53   $1,061.60   $1,061.60