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 $219.54   10.613%   $242.8398   $242.84   $242.85   $242.80  
  Purchase #2 $45.41   9.535%   $49.7398   $49.74   $49.75   $49.70  
  Purchase #3 $96.33   6.751%   $102.8332   $102.83   $102.85   $102.80  
  Purchase #4 $198.32   10.286%   $218.7192   $218.72   $218.70   $218.70  
  Purchase #5 $117.80   13.776%   $134.0281   $134.03   $134.05   $134.00  
  Purchase #6 $188.47   5.754%   $199.3146   $199.31   $199.30   $199.30  
  Purchase #7 $70.26   11.816%   $78.5619   $78.56   $78.55   $78.60  
  7 purchase totals = $936.13       $1,026.0366   $1,026.03   $1,026.05   $1,025.90