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 $156.39   12.680%   $176.2203   $176.22   $176.20   $176.20  
  Purchase #2 $217.66   13.294%   $246.5957   $246.60   $246.60   $246.60  
  Purchase #3 $59.39   5.425%   $62.6119   $62.61   $62.60   $62.60  
  Purchase #4 $82.65   13.799%   $94.0549   $94.05   $94.05   $94.10  
  Purchase #5 $13.88   5.118%   $14.5904   $14.59   $14.60   $14.60  
  Purchase #6 $137.98   4.651%   $144.3974   $144.40   $144.40   $144.40  
  Purchase #7 $25.43   12.572%   $28.6271   $28.63   $28.65   $28.60  
  7 purchase totals = $693.38       $767.0977   $767.10   $767.10   $767.10