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 $197.62   4.705%   $206.918   $206.92   $206.90   $206.90  
  Purchase #2 $92.53   7.727%   $99.6798   $99.68   $99.70   $99.70  
  Purchase #3 $109.99   7.701%   $118.4603   $118.46   $118.45   $118.50  
  Purchase #4 $228.85   5.216%   $240.7868   $240.79   $240.80   $240.80  
  Purchase #5 $22.35   10.277%   $24.6469   $24.65   $24.65   $24.60  
  Purchase #6 $119.86   12.539%   $134.8892   $134.89   $134.90   $134.90  
  Purchase #7 $77.68   7.380%   $83.4128   $83.41   $83.40   $83.40  
  7 purchase totals = $848.88       $908.7938   $908.80   $908.80   $908.80