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 $184.84   10.177%   $203.6512   $203.65   $203.65   $203.70  
  Purchase #2 $104.77   8.182%   $113.3423   $113.34   $113.35   $113.30  
  Purchase #3 $206.56   12.292%   $231.9504   $231.95   $231.95   $232.00  
  Purchase #4 $5.79   12.657%   $6.5228   $6.52   $6.50   $6.50  
  Purchase #5 $250.36   13.603%   $284.4165   $284.42   $284.40   $284.40  
  Purchase #6 $187.53   8.476%   $203.425   $203.43   $203.45   $203.40  
  Purchase #7 $187.26   10.297%   $206.5422   $206.54   $206.55   $206.50  
  7 purchase totals = $1,127.11       $1,249.8504   $1,249.85   $1,249.85   $1,249.80