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 $113.52   11.866%   $126.9903   $126.99   $127.00   $127.00  
  Purchase #2 $66.71   12.458%   $75.0207   $75.02   $75.00   $75.00  
  Purchase #3 $243.64   9.346%   $266.4106   $266.41   $266.40   $266.40  
  Purchase #4 $162.69   11.178%   $180.8755   $180.88   $180.90   $180.90  
  Purchase #5 $141.58   8.816%   $154.0617   $154.06   $154.05   $154.10  
  Purchase #6 $64.49   13.360%   $73.1059   $73.11   $73.10   $73.10  
  Purchase #7 $120.67   4.592%   $126.2112   $126.21   $126.20   $126.20  
  7 purchase totals = $913.30       $1,002.6759   $1,002.68   $1,002.65   $1,002.70