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 $30.48   7.147%   $32.6584   $32.66   $32.65   $32.70  
  Purchase #2 $101.25   4.294%   $105.5977   $105.60   $105.60   $105.60  
  Purchase #3 $188.86   3.628%   $195.7118   $195.71   $195.70   $195.70  
  Purchase #4 $179.90   13.427%   $204.0552   $204.06   $204.05   $204.10  
  Purchase #5 $232.74   8.773%   $253.1583   $253.16   $253.15   $253.20  
  Purchase #6 $60.73   5.606%   $64.1345   $64.13   $64.15   $64.10  
  Purchase #7 $162.73   5.111%   $171.0471   $171.05   $171.05   $171.00  
  7 purchase totals = $956.69       $1,026.3630   $1,026.37   $1,026.35   $1,026.40