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 $55.41   8.229%   $59.9697   $59.97   $59.95   $60.00  
  Purchase #2 $218.25   7.835%   $235.3499   $235.35   $235.35   $235.30  
  Purchase #3 $226.82   10.547%   $250.7427   $250.74   $250.75   $250.70  
  Purchase #4 $135.45   9.729%   $148.6279   $148.63   $148.65   $148.60  
  Purchase #5 $220.51   5.672%   $233.0173   $233.02   $233.00   $233.00  
  Purchase #6 $194.26   13.828%   $221.1223   $221.12   $221.10   $221.10  
  Purchase #7 $204.67   4.599%   $214.0828   $214.08   $214.10   $214.10  
  7 purchase totals = $1,255.37       $1,362.9126   $1,362.91   $1,362.90   $1,362.80