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 $10.38   5.178%   $10.9175   $10.92   $10.90   $10.90  
  Purchase #2 $221.52   3.736%   $229.796   $229.80   $229.80   $229.80  
  Purchase #3 $108.31   11.719%   $121.0028   $121.00   $121.00   $121.00  
  Purchase #4 $27.93   9.142%   $30.4834   $30.48   $30.50   $30.50  
  Purchase #5 $5.42   4.153%   $5.6451   $5.65   $5.65   $5.60  
  Purchase #6 $243.35   12.619%   $274.0583   $274.06   $274.05   $274.10  
  Purchase #7 $103.62   5.219%   $109.0279   $109.03   $109.05   $109.00  
  7 purchase totals = $720.53       $780.9310   $780.94   $780.95   $780.90