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 $84.94   9.719%   $93.1953   $93.20   $93.20   $93.20  
  Purchase #2 $128.89   8.573%   $139.9397   $139.94   $139.95   $139.90  
  Purchase #3 $224.34   11.313%   $249.7196   $249.72   $249.70   $249.70  
  Purchase #4 $221.83   6.492%   $236.2312   $236.23   $236.25   $236.20  
  Purchase #5 $180.35   12.248%   $202.4393   $202.44   $202.45   $202.40  
  Purchase #6 $81.29   8.217%   $87.9696   $87.97   $87.95   $88.00  
  Purchase #7 $213.75   4.659%   $223.7086   $223.71   $223.70   $223.70  
  7 purchase totals = $1,135.39       $1,233.2033   $1,233.21   $1,233.20   $1,233.10