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 $42.82   3.793%   $44.4442   $44.44   $44.45   $44.40  
  Purchase #2 $104.37   10.685%   $115.5219   $115.52   $115.50   $115.50  
  Purchase #3 $55.92   5.862%   $59.198   $59.20   $59.20   $59.20  
  Purchase #4 $231.85   8.548%   $251.6685   $251.67   $251.65   $251.70  
  Purchase #5 $175.40   9.655%   $192.3349   $192.33   $192.35   $192.30  
  Purchase #6 $128.95   5.651%   $136.237   $136.24   $136.25   $136.20  
  Purchase #7 $223.91   3.166%   $230.999   $231.00   $231.00   $231.00  
  7 purchase totals = $963.22       $1,030.4035   $1,030.40   $1,030.40   $1,030.30