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 $94.67   9.311%   $103.4847   $103.48   $103.50   $103.50  
  Purchase #2 $181.52   5.252%   $191.0534   $191.05   $191.05   $191.10  
  Purchase #3 $195.55   3.164%   $201.7372   $201.74   $201.75   $201.70  
  Purchase #4 $200.42   13.112%   $226.6991   $226.70   $226.70   $226.70  
  Purchase #5 $39.54   8.422%   $42.8701   $42.87   $42.85   $42.90  
  Purchase #6 $189.95   4.491%   $198.4807   $198.48   $198.50   $198.50  
  Purchase #7 $56.95   13.121%   $64.4224   $64.42   $64.40   $64.40  
  7 purchase totals = $958.60       $1,028.7476   $1,028.74   $1,028.75   $1,028.80