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 $162.58   5.148%   $170.9496   $170.95   $170.95   $170.90  
  Purchase #2 $83.42   12.149%   $93.5547   $93.55   $93.55   $93.60  
  Purchase #3 $56.93   10.412%   $62.8576   $62.86   $62.85   $62.90  
  Purchase #4 $231.63   3.164%   $238.9588   $238.96   $238.95   $239.00  
  Purchase #5 $145.91   9.772%   $160.1683   $160.17   $160.15   $160.20  
  Purchase #6 $192.58   5.197%   $202.5884   $202.59   $202.60   $202.60  
  Purchase #7 $102.41   3.120%   $105.6052   $105.61   $105.60   $105.60  
  7 purchase totals = $975.46       $1,034.6826   $1,034.69   $1,034.65   $1,034.80