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 $181.56   6.662%   $193.6555   $193.66   $193.65   $193.70  
  Purchase #2 $30.78   13.115%   $34.8168   $34.82   $34.80   $34.80  
  Purchase #3 $165.38   12.481%   $186.0211   $186.02   $186.00   $186.00  
  Purchase #4 $197.45   6.709%   $210.6969   $210.70   $210.70   $210.70  
  Purchase #5 $197.99   10.261%   $218.3058   $218.31   $218.30   $218.30  
  Purchase #6 $65.61   7.765%   $70.7046   $70.70   $70.70   $70.70  
  Purchase #7 $40.41   6.515%   $43.0427   $43.04   $43.05   $43.00  
  7 purchase totals = $879.18       $957.2434   $957.25   $957.20   $957.20