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 $82.72   4.716%   $86.6211   $86.62   $86.60   $86.60  
  Purchase #2 $220.96   13.735%   $251.3089   $251.31   $251.30   $251.30  
  Purchase #3 $152.32   13.650%   $173.1117   $173.11   $173.10   $173.10  
  Purchase #4 $107.25   3.206%   $110.6884   $110.69   $110.70   $110.70  
  Purchase #5 $183.69   10.142%   $202.3198   $202.32   $202.30   $202.30  
  Purchase #6 $170.85   9.811%   $187.6121   $187.61   $187.60   $187.60  
  Purchase #7 $239.89   9.643%   $263.0226   $263.02   $263.00   $263.00  
  7 purchase totals = $1,157.68       $1,274.6846   $1,274.68   $1,274.60   $1,274.60