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 $58.59   5.758%   $61.9636   $61.96   $61.95   $62.00  
  Purchase #2 $212.79   11.215%   $236.6544   $236.65   $236.65   $236.70  
  Purchase #3 $86.97   4.568%   $90.9428   $90.94   $90.95   $90.90  
  Purchase #4 $193.41   4.221%   $201.5738   $201.57   $201.55   $201.60  
  Purchase #5 $69.80   8.336%   $75.6185   $75.62   $75.60   $75.60  
  Purchase #6 $164.30   12.335%   $184.5664   $184.57   $184.55   $184.60  
  Purchase #7 $130.67   13.121%   $147.8152   $147.82   $147.80   $147.80  
  7 purchase totals = $916.53       $999.1347   $999.13   $999.05   $999.20