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 $57.61   8.610%   $62.5702   $62.57   $62.55   $62.60  
  Purchase #2 $131.35   5.422%   $138.4718   $138.47   $138.45   $138.50  
  Purchase #3 $69.47   8.721%   $75.5285   $75.53   $75.55   $75.50  
  Purchase #4 $147.39   9.807%   $161.8445   $161.84   $161.85   $161.80  
  Purchase #5 $5.57   7.869%   $6.0083   $6.01   $6.00   $6.00  
  Purchase #6 $78.67   10.673%   $87.0664   $87.07   $87.05   $87.10  
  Purchase #7 $249.36   6.608%   $265.8377   $265.84   $265.85   $265.80  
  7 purchase totals = $739.42       $797.3274   $797.33   $797.30   $797.30