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 $188.60   8.507%   $204.6442   $204.64   $204.65   $204.60  
  Purchase #2 $110.60   4.577%   $115.6622   $115.66   $115.65   $115.70  
  Purchase #3 $70.30   6.603%   $74.9419   $74.94   $74.95   $74.90  
  Purchase #4 $96.46   13.731%   $109.7049   $109.70   $109.70   $109.70  
  Purchase #5 $186.76   13.313%   $211.6234   $211.62   $211.60   $211.60  
  Purchase #6 $247.79   3.589%   $256.6832   $256.68   $256.70   $256.70  
  Purchase #7 $56.74   3.763%   $58.8751   $58.88   $58.90   $58.90  
  7 purchase totals = $957.25       $1,032.1349   $1,032.12   $1,032.15   $1,032.10