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 $56.85   5.680%   $60.0791   $60.08   $60.10   $60.10  
  Purchase #2 $118.59   5.109%   $124.6488   $124.65   $124.65   $124.60  
  Purchase #3 $73.94   4.367%   $77.169   $77.17   $77.15   $77.20  
  Purchase #4 $222.56   13.114%   $251.7465   $251.75   $251.75   $251.70  
  Purchase #5 $20.33   13.145%   $23.0024   $23.00   $23.00   $23.00  
  Purchase #6 $160.43   6.404%   $170.7039   $170.70   $170.70   $170.70  
  Purchase #7 $47.98   13.581%   $54.4962   $54.50   $54.50   $54.50  
  7 purchase totals = $700.68       $761.8459   $761.85   $761.85   $761.80