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 $128.83   10.234%   $142.0145   $142.01   $142.00   $142.00  
  Purchase #2 $61.70   9.103%   $67.3166   $67.32   $67.30   $67.30  
  Purchase #3 $187.46   7.681%   $201.8588   $201.86   $201.85   $201.90  
  Purchase #4 $242.95   4.281%   $253.3507   $253.35   $253.35   $253.40  
  Purchase #5 $15.88   10.858%   $17.6043   $17.60   $17.60   $17.60  
  Purchase #6 $167.84   3.641%   $173.9511   $173.95   $173.95   $174.00  
  Purchase #7 $170.61   11.264%   $189.8275   $189.83   $189.85   $189.80  
  7 purchase totals = $975.27       $1,045.9235   $1,045.92   $1,045.90   $1,046.00