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 $175.91   6.112%   $186.6616   $186.66   $186.65   $186.70  
  Purchase #2 $235.67   6.832%   $251.771   $251.77   $251.75   $251.80  
  Purchase #3 $155.72   9.740%   $170.8871   $170.89   $170.90   $170.90  
  Purchase #4 $184.46   9.762%   $202.467   $202.47   $202.45   $202.50  
  Purchase #5 $94.29   11.857%   $105.47   $105.47   $105.45   $105.50  
  Purchase #6 $58.75   5.551%   $62.0112   $62.01   $62.00   $62.00  
  Purchase #7 $5.48   12.539%   $6.1671   $6.17   $6.15   $6.20  
  7 purchase totals = $910.28       $985.4350   $985.44   $985.35   $985.60