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 $64.60   5.708%   $68.2874   $68.29   $68.30   $68.30  
  Purchase #2 $79.93   4.220%   $83.303   $83.30   $83.30   $83.30  
  Purchase #3 $236.47   12.805%   $266.75   $266.75   $266.75   $266.80  
  Purchase #4 $76.92   3.377%   $79.5176   $79.52   $79.50   $79.50  
  Purchase #5 $143.34   5.830%   $151.6967   $151.70   $151.70   $151.70  
  Purchase #6 $220.77   12.318%   $247.9644   $247.96   $247.95   $248.00  
  Purchase #7 $156.32   6.747%   $166.8669   $166.87   $166.85   $166.90  
  7 purchase totals = $978.35       $1,064.3860   $1,064.39   $1,064.35   $1,064.50