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 $198.95   3.619%   $206.15   $206.15   $206.15   $206.20  
  Purchase #2 $91.32   4.652%   $95.5682   $95.57   $95.55   $95.60  
  Purchase #3 $189.65   11.685%   $211.8106   $211.81   $211.80   $211.80  
  Purchase #4 $124.39   11.572%   $138.7844   $138.78   $138.80   $138.80  
  Purchase #5 $66.67   12.824%   $75.2198   $75.22   $75.20   $75.20  
  Purchase #6 $178.95   7.123%   $191.6966   $191.70   $191.70   $191.70  
  Purchase #7 $234.51   3.197%   $242.0073   $242.01   $242.00   $242.00  
  7 purchase totals = $1,084.44       $1,161.2369   $1,161.24   $1,161.20   $1,161.30