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 $110.95   10.464%   $122.5598   $122.56   $122.55   $122.60  
  Purchase #2 $157.62   11.442%   $175.6549   $175.65   $175.65   $175.70  
  Purchase #3 $14.40   9.384%   $15.7513   $15.75   $15.75   $15.80  
  Purchase #4 $25.94   3.751%   $26.913   $26.91   $26.90   $26.90  
  Purchase #5 $116.46   7.369%   $125.0419   $125.04   $125.05   $125.00  
  Purchase #6 $85.46   3.483%   $88.4366   $88.44   $88.45   $88.40  
  Purchase #7 $223.84   3.495%   $231.6632   $231.66   $231.65   $231.70  
  7 purchase totals = $734.67       $786.0207   $786.01   $786.00   $786.10