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 $194.74   5.278%   $205.0184   $205.02   $205.00   $205.00  
  Purchase #2 $59.62   7.558%   $64.1261   $64.13   $64.15   $64.10  
  Purchase #3 $171.32   10.712%   $189.6718   $189.67   $189.65   $189.70  
  Purchase #4 $165.63   7.158%   $177.4858   $177.49   $177.50   $177.50  
  Purchase #5 $143.92   5.481%   $151.8083   $151.81   $151.80   $151.80  
  Purchase #6 $97.53   12.335%   $109.5603   $109.56   $109.55   $109.60  
  Purchase #7 $189.56   12.741%   $213.7118   $213.71   $213.70   $213.70  
  7 purchase totals = $1,022.32       $1,111.3825   $1,111.39   $1,111.35   $1,111.40