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 $61.78   6.793%   $65.9767   $65.98   $66.00   $66.00  
  Purchase #2 $138.30   12.197%   $155.1685   $155.17   $155.15   $155.20  
  Purchase #3 $236.52   9.201%   $258.2822   $258.28   $258.30   $258.30  
  Purchase #4 $236.58   9.148%   $258.2223   $258.22   $258.20   $258.20  
  Purchase #5 $93.97   10.574%   $103.9064   $103.91   $103.90   $103.90  
  Purchase #6 $245.68   10.530%   $271.5501   $271.55   $271.55   $271.60  
  Purchase #7 $160.64   7.346%   $172.4406   $172.44   $172.45   $172.40  
  7 purchase totals = $1,173.47       $1,285.5468   $1,285.55   $1,285.55   $1,285.60