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 $60.97   3.427%   $63.0594   $63.06   $63.05   $63.10  
  Purchase #2 $242.43   3.516%   $250.9538   $250.95   $250.95   $251.00  
  Purchase #3 $123.65   5.518%   $130.473   $130.47   $130.45   $130.50  
  Purchase #4 $122.74   12.818%   $138.4728   $138.47   $138.45   $138.50  
  Purchase #5 $128.98   3.820%   $133.907   $133.91   $133.90   $133.90  
  Purchase #6 $12.88   11.700%   $14.387   $14.39   $14.40   $14.40  
  Purchase #7 $17.34   11.871%   $19.3984   $19.40   $19.40   $19.40  
  7 purchase totals = $708.99       $750.6514   $750.65   $750.60   $750.80