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 $188.86   9.869%   $207.4986   $207.50   $207.50   $207.50  
  Purchase #2 $210.84   11.775%   $235.6664   $235.67   $235.65   $235.70  
  Purchase #3 $175.29   13.776%   $199.438   $199.44   $199.45   $199.40  
  Purchase #4 $30.89   8.425%   $33.4925   $33.49   $33.50   $33.50  
  Purchase #5 $128.28   12.495%   $144.3086   $144.31   $144.30   $144.30  
  Purchase #6 $203.50   6.157%   $216.0295   $216.03   $216.05   $216.00  
  Purchase #7 $8.50   11.746%   $9.4984   $9.50   $9.50   $9.50  
  7 purchase totals = $946.16       $1,045.9320   $1,045.94   $1,045.95   $1,045.90