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 $118.34   4.164%   $123.2677   $123.27   $123.25   $123.30  
  Purchase #2 $173.72   3.615%   $180   $180.00   $180.00   $180.00  
  Purchase #3 $185.62   9.383%   $203.0367   $203.04   $203.05   $203.00  
  Purchase #4 $219.73   5.785%   $232.4414   $232.44   $232.45   $232.40  
  Purchase #5 $221.83   11.281%   $246.8546   $246.85   $246.85   $246.90  
  Purchase #6 $181.54   10.257%   $200.1606   $200.16   $200.15   $200.20  
  Purchase #7 $12.67   12.265%   $14.224   $14.22   $14.20   $14.20  
  7 purchase totals = $1,113.45       $1,199.9850   $1,199.98   $1,199.95   $1,200.00