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 $215.79   10.262%   $237.9344   $237.93   $237.95   $237.90  
  Purchase #2 $8.68   11.720%   $9.6973   $9.70   $9.70   $9.70  
  Purchase #3 $71.25   7.576%   $76.6479   $76.65   $76.65   $76.60  
  Purchase #4 $241.45   6.829%   $257.9386   $257.94   $257.95   $257.90  
  Purchase #5 $180.66   7.207%   $193.6802   $193.68   $193.70   $193.70  
  Purchase #6 $138.40   5.313%   $145.7532   $145.75   $145.75   $145.80  
  Purchase #7 $95.57   9.271%   $104.4303   $104.43   $104.45   $104.40  
  7 purchase totals = $951.80       $1,026.0819   $1,026.08   $1,026.15   $1,026.00