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 $200.57   8.202%   $217.0208   $217.02   $217.00   $217.00  
  Purchase #2 $212.52   3.725%   $220.4364   $220.44   $220.45   $220.40  
  Purchase #3 $147.94   3.137%   $152.5809   $152.58   $152.60   $152.60  
  Purchase #4 $209.99   3.865%   $218.1061   $218.11   $218.10   $218.10  
  Purchase #5 $214.98   4.326%   $224.28   $224.28   $224.30   $224.30  
  Purchase #6 $185.64   4.385%   $193.7803   $193.78   $193.80   $193.80  
  Purchase #7 $90.59   9.314%   $99.0276   $99.03   $99.05   $99.00  
  7 purchase totals = $1,262.23       $1,325.2321   $1,325.24   $1,325.30   $1,325.20