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 $189.67   4.143%   $197.528   $197.53   $197.55   $197.50  
  Purchase #2 $216.39   4.704%   $226.569   $226.57   $226.55   $226.60  
  Purchase #3 $148.96   7.839%   $160.637   $160.64   $160.65   $160.60  
  Purchase #4 $163.55   7.688%   $176.1237   $176.12   $176.10   $176.10  
  Purchase #5 $221.41   13.327%   $250.9173   $250.92   $250.90   $250.90  
  Purchase #6 $243.33   9.317%   $266.0011   $266.00   $266.00   $266.00  
  Purchase #7 $50.89   5.762%   $53.8223   $53.82   $53.80   $53.80  
  7 purchase totals = $1,234.20       $1,331.5984   $1,331.60   $1,331.55   $1,331.50