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 $40.53   8.779%   $44.0881   $44.09   $44.10   $44.10  
  Purchase #2 $228.92   9.264%   $250.1271   $250.13   $250.15   $250.10  
  Purchase #3 $169.28   9.221%   $184.8893   $184.89   $184.90   $184.90  
  Purchase #4 $157.40   12.727%   $177.4323   $177.43   $177.45   $177.40  
  Purchase #5 $82.26   6.342%   $87.4769   $87.48   $87.50   $87.50  
  Purchase #6 $69.33   8.627%   $75.3111   $75.31   $75.30   $75.30  
  Purchase #7 $135.80   5.852%   $143.747   $143.75   $143.75   $143.70  
  7 purchase totals = $883.52       $963.0718   $963.08   $963.15   $963.00