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 $248.75   9.452%   $272.2619   $272.26   $272.25   $272.30  
  Purchase #2 $203.29   4.141%   $211.7082   $211.71   $211.70   $211.70  
  Purchase #3 $223.35   5.571%   $235.7928   $235.79   $235.80   $235.80  
  Purchase #4 $35.83   11.189%   $39.839   $39.84   $39.85   $39.80  
  Purchase #5 $62.48   4.196%   $65.1017   $65.10   $65.10   $65.10  
  Purchase #6 $226.33   4.265%   $235.983   $235.98   $236.00   $236.00  
  Purchase #7 $204.54   7.178%   $219.2219   $219.22   $219.20   $219.20  
  7 purchase totals = $1,204.57       $1,279.9085   $1,279.90   $1,279.90   $1,279.90