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 $56.26   5.558%   $59.3869   $59.39   $59.40   $59.40  
  Purchase #2 $249.27   7.353%   $267.5988   $267.60   $267.60   $267.60  
  Purchase #3 $17.76   5.785%   $18.7874   $18.79   $18.80   $18.80  
  Purchase #4 $187.82   11.199%   $208.854   $208.85   $208.85   $208.90  
  Purchase #5 $223.65   8.473%   $242.5999   $242.60   $242.60   $242.60  
  Purchase #6 $28.52   5.213%   $30.0067   $30.01   $30.00   $30.00  
  Purchase #7 $29.52   7.388%   $31.7009   $31.70   $31.70   $31.70  
  7 purchase totals = $792.80       $858.9346   $858.94   $858.95   $859.00