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 $82.48   12.829%   $93.0614   $93.06   $93.05   $93.10  
  Purchase #2 $96.55   10.242%   $106.4387   $106.44   $106.45   $106.40  
  Purchase #3 $122.71   10.104%   $135.1086   $135.11   $135.10   $135.10  
  Purchase #4 $44.37   11.757%   $49.5866   $49.59   $49.60   $49.60  
  Purchase #5 $206.50   13.476%   $234.3279   $234.33   $234.35   $234.30  
  Purchase #6 $205.44   13.315%   $232.7943   $232.79   $232.80   $232.80  
  Purchase #7 $228.91   12.814%   $258.2425   $258.24   $258.25   $258.20  
  7 purchase totals = $986.96       $1,109.5600   $1,109.56   $1,109.60   $1,109.50