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 $67.46   12.425%   $75.8419   $75.84   $75.85   $75.80  
  Purchase #2 $232.64   7.585%   $250.2857   $250.29   $250.30   $250.30  
  Purchase #3 $172.84   7.242%   $185.3571   $185.36   $185.35   $185.40  
  Purchase #4 $41.93   5.310%   $44.1565   $44.16   $44.15   $44.20  
  Purchase #5 $23.64   4.738%   $24.7601   $24.76   $24.75   $24.80  
  Purchase #6 $167.76   3.692%   $173.9537   $173.95   $173.95   $174.00  
  Purchase #7 $245.47   3.804%   $254.8077   $254.81   $254.80   $254.80  
  7 purchase totals = $951.74       $1,009.1627   $1,009.17   $1,009.15   $1,009.30