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 $63.43   3.674%   $65.7604   $65.76   $65.75   $65.80  
  Purchase #2 $91.74   4.818%   $96.16   $96.16   $96.15   $96.20  
  Purchase #3 $6.84   12.613%   $7.7027   $7.70   $7.70   $7.70  
  Purchase #4 $224.31   5.167%   $235.9001   $235.90   $235.90   $235.90  
  Purchase #5 $233.41   3.180%   $240.8324   $240.83   $240.85   $240.80  
  Purchase #6 $111.34   11.579%   $124.2321   $124.23   $124.25   $124.20  
  Purchase #7 $242.95   4.799%   $254.6092   $254.61   $254.60   $254.60  
  7 purchase totals = $974.02       $1,025.1969   $1,025.19   $1,025.20   $1,025.20