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 $193.84   6.556%   $206.5482   $206.55   $206.55   $206.50  
  Purchase #2 $67.41   5.676%   $71.2362   $71.24   $71.25   $71.20  
  Purchase #3 $14.48   10.564%   $16.0097   $16.01   $16.00   $16.00  
  Purchase #4 $229.71   11.737%   $256.6711   $256.67   $256.65   $256.70  
  Purchase #5 $211.50   5.158%   $222.4092   $222.41   $222.40   $222.40  
  Purchase #6 $179.95   13.525%   $204.2882   $204.29   $204.30   $204.30  
  Purchase #7 $160.36   6.725%   $171.1442   $171.14   $171.15   $171.10  
  7 purchase totals = $1,057.25       $1,148.3068   $1,148.31   $1,148.30   $1,148.20