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 $173.95   10.236%   $191.7555   $191.76   $191.75   $191.80  
  Purchase #2 $49.79   10.523%   $55.0294   $55.03   $55.05   $55.00  
  Purchase #3 $50.51   9.493%   $55.3049   $55.30   $55.30   $55.30  
  Purchase #4 $228.36   9.651%   $250.399   $250.40   $250.40   $250.40  
  Purchase #5 $224.57   3.199%   $231.754   $231.75   $231.75   $231.80  
  Purchase #6 $128.85   6.636%   $137.4005   $137.40   $137.40   $137.40  
  Purchase #7 $118.73   7.775%   $127.9613   $127.96   $127.95   $128.00  
  7 purchase totals = $974.76       $1,049.6046   $1,049.60   $1,049.60   $1,049.70