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 $68.49   9.482%   $74.9842   $74.98   $75.00   $75.00  
  Purchase #2 $243.65   3.697%   $252.6577   $252.66   $252.65   $252.70  
  Purchase #3 $27.25   10.823%   $30.1993   $30.20   $30.20   $30.20  
  Purchase #4 $83.34   7.739%   $89.7897   $89.79   $89.80   $89.80  
  Purchase #5 $176.30   9.610%   $193.2424   $193.24   $193.25   $193.20  
  Purchase #6 $196.84   4.713%   $206.1171   $206.12   $206.10   $206.10  
  Purchase #7 $81.51   7.852%   $87.9102   $87.91   $87.90   $87.90  
  7 purchase totals = $877.38       $934.9006   $934.90   $934.90   $934.90