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 $193.63   5.612%   $204.4965   $204.50   $204.50   $204.50  
  Purchase #2 $89.25   8.453%   $96.7943   $96.79   $96.80   $96.80  
  Purchase #3 $203.49   7.678%   $219.114   $219.11   $219.10   $219.10  
  Purchase #4 $79.50   4.476%   $83.0584   $83.06   $83.05   $83.10  
  Purchase #5 $82.42   12.440%   $92.673   $92.67   $92.65   $92.70  
  Purchase #6 $133.83   3.561%   $138.5957   $138.60   $138.60   $138.60  
  Purchase #7 $194.82   3.130%   $200.9179   $200.92   $200.90   $200.90  
  7 purchase totals = $976.94       $1,035.6498   $1,035.65   $1,035.60   $1,035.70