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 $167.96   10.326%   $185.3035   $185.30   $185.30   $185.30  
  Purchase #2 $51.49   4.106%   $53.6042   $53.60   $53.60   $53.60  
  Purchase #3 $235.98   13.318%   $267.4078   $267.41   $267.40   $267.40  
  Purchase #4 $202.75   13.154%   $229.4197   $229.42   $229.40   $229.40  
  Purchase #5 $115.65   7.201%   $123.978   $123.98   $124.00   $124.00  
  Purchase #6 $80.92   7.345%   $86.8636   $86.86   $86.85   $86.90  
  Purchase #7 $226.99   6.591%   $241.9509   $241.95   $241.95   $242.00  
  7 purchase totals = $1,081.74       $1,188.5277   $1,188.52   $1,188.50   $1,188.60