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 $12.90   9.345%   $14.1055   $14.11   $14.10   $14.10  
  Purchase #2 $28.52   5.245%   $30.0159   $30.02   $30.00   $30.00  
  Purchase #3 $240.39   8.472%   $260.7558   $260.76   $260.75   $260.80  
  Purchase #4 $194.56   12.774%   $219.4131   $219.41   $219.40   $219.40  
  Purchase #5 $211.64   12.283%   $237.6357   $237.64   $237.65   $237.60  
  Purchase #6 $134.85   5.393%   $142.1225   $142.12   $142.10   $142.10  
  Purchase #7 $232.89   11.620%   $259.9518   $259.95   $259.95   $260.00  
  7 purchase totals = $1,055.75       $1,164.0003   $1,164.01   $1,163.95   $1,164.00