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 $234.63   3.867%   $243.7031   $243.70   $243.70   $243.70  
  Purchase #2 $220.61   6.650%   $235.2806   $235.28   $235.30   $235.30  
  Purchase #3 $34.61   4.170%   $36.0532   $36.05   $36.05   $36.10  
  Purchase #4 $29.72   4.319%   $31.0036   $31.00   $31.00   $31.00  
  Purchase #5 $197.78   9.184%   $215.9441   $215.94   $215.95   $215.90  
  Purchase #6 $53.73   3.564%   $55.6449   $55.64   $55.65   $55.60  
  Purchase #7 $194.91   7.386%   $209.3061   $209.31   $209.30   $209.30  
  7 purchase totals = $965.99       $1,026.9356   $1,026.92   $1,026.95   $1,026.90