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 $163.57   12.336%   $183.748   $183.75   $183.75   $183.70  
  Purchase #2 $101.61   10.655%   $112.4365   $112.44   $112.45   $112.40  
  Purchase #3 $224.25   10.351%   $247.4621   $247.46   $247.45   $247.50  
  Purchase #4 $201.65   11.737%   $225.3177   $225.32   $225.30   $225.30  
  Purchase #5 $22.89   8.519%   $24.84   $24.84   $24.85   $24.80  
  Purchase #6 $129.31   12.481%   $145.4492   $145.45   $145.45   $145.40  
  Purchase #7 $139.46   8.297%   $151.031   $151.03   $151.05   $151.00  
  7 purchase totals = $982.74       $1,090.2845   $1,090.29   $1,090.30   $1,090.10