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 $153.65   8.706%   $167.0268   $167.03   $167.05   $167.00  
  Purchase #2 $173.43   10.378%   $191.4286   $191.43   $191.45   $191.40  
  Purchase #3 $53.53   12.133%   $60.0248   $60.02   $60.00   $60.00  
  Purchase #4 $130.33   7.406%   $139.9822   $139.98   $140.00   $140.00  
  Purchase #5 $72.36   11.857%   $80.9397   $80.94   $80.95   $80.90  
  Purchase #6 $219.66   3.507%   $227.3635   $227.36   $227.35   $227.40  
  Purchase #7 $191.70   13.708%   $217.9782   $217.98   $218.00   $218.00  
  7 purchase totals = $994.66       $1,084.7438   $1,084.74   $1,084.80   $1,084.70