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 $12.43   13.663%   $14.1283   $14.13   $14.15   $14.10  
  Purchase #2 $117.52   12.205%   $131.8633   $131.86   $131.85   $131.90  
  Purchase #3 $180.76   9.385%   $197.7243   $197.72   $197.70   $197.70  
  Purchase #4 $195.69   12.412%   $219.979   $219.98   $220.00   $220.00  
  Purchase #5 $147.34   8.872%   $160.412   $160.41   $160.40   $160.40  
  Purchase #6 $243.41   9.557%   $266.6727   $266.67   $266.65   $266.70  
  Purchase #7 $215.79   10.839%   $239.1795   $239.18   $239.20   $239.20  
  7 purchase totals = $1,112.94       $1,229.9591   $1,229.95   $1,229.95   $1,230.00