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 $201.73   8.541%   $218.9598   $218.96   $218.95   $219.00  
  Purchase #2 $190.31   6.280%   $202.2615   $202.26   $202.25   $202.30  
  Purchase #3 $32.41   9.517%   $35.4945   $35.49   $35.50   $35.50  
  Purchase #4 $231.32   4.438%   $241.586   $241.59   $241.60   $241.60  
  Purchase #5 $39.76   4.761%   $41.653   $41.65   $41.65   $41.70  
  Purchase #6 $180.80   5.154%   $190.1184   $190.12   $190.10   $190.10  
  Purchase #7 $63.70   12.696%   $71.7874   $71.79   $71.80   $71.80  
  7 purchase totals = $940.03       $1,001.8606   $1,001.86   $1,001.85   $1,002.00