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 $95.98   10.753%   $106.3007   $106.30   $106.30   $106.30  
  Purchase #2 $249.27   11.478%   $277.8812   $277.88   $277.90   $277.90  
  Purchase #3 $28.77   12.124%   $32.2581   $32.26   $32.25   $32.30  
  Purchase #4 $90.48   11.450%   $100.84   $100.84   $100.85   $100.80  
  Purchase #5 $178.47   5.621%   $188.5018   $188.50   $188.50   $188.50  
  Purchase #6 $203.46   11.404%   $226.6626   $226.66   $226.65   $226.70  
  Purchase #7 $146.95   11.188%   $163.3908   $163.39   $163.40   $163.40  
  7 purchase totals = $993.38       $1,095.8352   $1,095.83   $1,095.85   $1,095.90