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 $181.83   11.669%   $203.0477   $203.05   $203.05   $203.00  
  Purchase #2 $184.62   12.479%   $207.6587   $207.66   $207.65   $207.70  
  Purchase #3 $203.81   12.695%   $229.6837   $229.68   $229.70   $229.70  
  Purchase #4 $119.54   9.596%   $131.0111   $131.01   $131.00   $131.00  
  Purchase #5 $100.72   10.709%   $111.5061   $111.51   $111.50   $111.50  
  Purchase #6 $69.93   12.539%   $78.6985   $78.70   $78.70   $78.70  
  Purchase #7 $194.71   9.855%   $213.8987   $213.90   $213.90   $213.90  
  7 purchase totals = $1,055.16       $1,175.5045   $1,175.51   $1,175.50   $1,175.50