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 $59.31   13.524%   $67.3311   $67.33   $67.35   $67.30  
  Purchase #2 $165.72   12.590%   $186.5841   $186.58   $186.60   $186.60  
  Purchase #3 $61.99   4.761%   $64.9413   $64.94   $64.95   $64.90  
  Purchase #4 $214.84   11.654%   $239.8775   $239.88   $239.90   $239.90  
  Purchase #5 $95.86   13.248%   $108.5595   $108.56   $108.55   $108.60  
  Purchase #6 $187.71   3.230%   $193.773   $193.77   $193.75   $193.80  
  Purchase #7 $168.93   10.273%   $186.2842   $186.28   $186.30   $186.30  
  7 purchase totals = $954.36       $1,047.3507   $1,047.34   $1,047.40   $1,047.40