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 $78.94   6.726%   $84.2495   $84.25   $84.25   $84.20  
  Purchase #2 $99.63   10.690%   $110.2804   $110.28   $110.30   $110.30  
  Purchase #3 $28.54   10.499%   $31.5364   $31.54   $31.55   $31.50  
  Purchase #4 $208.47   8.323%   $225.821   $225.82   $225.80   $225.80  
  Purchase #5 $240.28   4.310%   $250.6361   $250.64   $250.65   $250.60  
  Purchase #6 $229.45   12.623%   $258.4135   $258.41   $258.40   $258.40  
  Purchase #7 $41.27   9.841%   $45.3314   $45.33   $45.35   $45.30  
  7 purchase totals = $926.58       $1,006.2683   $1,006.27   $1,006.30   $1,006.10