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 $147.38   5.521%   $155.5168   $155.52   $155.50   $155.50  
  Purchase #2 $62.86   8.268%   $68.0573   $68.06   $68.05   $68.10  
  Purchase #3 $227.49   11.463%   $253.5672   $253.57   $253.55   $253.60  
  Purchase #4 $236.40   8.137%   $255.6359   $255.64   $255.65   $255.60  
  Purchase #5 $79.42   13.710%   $90.3085   $90.31   $90.30   $90.30  
  Purchase #6 $162.31   8.297%   $175.7769   $175.78   $175.80   $175.80  
  Purchase #7 $23.90   8.780%   $25.9984   $26.00   $26.00   $26.00  
  7 purchase totals = $939.76       $1,024.8610   $1,024.88   $1,024.85   $1,024.90