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 $189.53   13.418%   $214.9611   $214.96   $214.95   $215.00  
  Purchase #2 $96.75   8.182%   $104.6661   $104.67   $104.65   $104.70  
  Purchase #3 $154.90   6.825%   $165.4719   $165.47   $165.45   $165.50  
  Purchase #4 $17.97   7.671%   $19.3485   $19.35   $19.35   $19.30  
  Purchase #5 $192.84   5.828%   $204.0787   $204.08   $204.10   $204.10  
  Purchase #6 $149.44   9.502%   $163.6398   $163.64   $163.65   $163.60  
  Purchase #7 $60.59   4.573%   $63.3608   $63.36   $63.35   $63.40  
  7 purchase totals = $862.02       $935.5269   $935.53   $935.50   $935.60