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 $164.31   13.563%   $186.5954   $186.60   $186.60   $186.60  
  Purchase #2 $98.88   11.498%   $110.2492   $110.25   $110.25   $110.20  
  Purchase #3 $74.39   11.849%   $83.2045   $83.20   $83.20   $83.20  
  Purchase #4 $53.26   13.427%   $60.4112   $60.41   $60.40   $60.40  
  Purchase #5 $185.87   12.631%   $209.3472   $209.35   $209.35   $209.30  
  Purchase #6 $121.46   8.717%   $132.0477   $132.05   $132.05   $132.00  
  Purchase #7 $236.67   12.457%   $266.152   $266.15   $266.15   $266.20  
  7 purchase totals = $934.84       $1,048.0072   $1,048.01   $1,048.00   $1,047.90