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 $36.91   11.747%   $41.2458   $41.25   $41.25   $41.20  
  Purchase #2 $46.57   7.104%   $49.8783   $49.88   $49.90   $49.90  
  Purchase #3 $180.94   5.558%   $190.9966   $191.00   $191.00   $191.00  
  Purchase #4 $212.36   6.365%   $225.8767   $225.88   $225.90   $225.90  
  Purchase #5 $138.29   4.409%   $144.3872   $144.39   $144.40   $144.40  
  Purchase #6 $63.49   7.242%   $68.0879   $68.09   $68.10   $68.10  
  Purchase #7 $190.32   8.742%   $206.9578   $206.96   $206.95   $207.00  
  7 purchase totals = $868.88       $927.4303   $927.45   $927.50   $927.50