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 $54.87   11.517%   $61.1894   $61.19   $61.20   $61.20  
  Purchase #2 $138.99   13.280%   $157.4479   $157.45   $157.45   $157.40  
  Purchase #3 $37.34   3.713%   $38.7264   $38.73   $38.75   $38.70  
  Purchase #4 $37.46   6.300%   $39.82   $39.82   $39.80   $39.80  
  Purchase #5 $191.68   7.448%   $205.9563   $205.96   $205.95   $206.00  
  Purchase #6 $135.60   3.778%   $140.723   $140.72   $140.70   $140.70  
  Purchase #7 $106.64   9.478%   $116.7473   $116.75   $116.75   $116.70  
  7 purchase totals = $702.58       $760.6103   $760.62   $760.60   $760.50