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 $63.35   5.754%   $66.9952   $67.00   $67.00   $67.00  
  Purchase #2 $232.68   9.846%   $255.5897   $255.59   $255.60   $255.60  
  Purchase #3 $226.29   12.531%   $254.6464   $254.65   $254.65   $254.60  
  Purchase #4 $233.31   8.551%   $253.2603   $253.26   $253.25   $253.30  
  Purchase #5 $22.52   7.458%   $24.1995   $24.20   $24.20   $24.20  
  Purchase #6 $38.60   9.357%   $42.2118   $42.21   $42.20   $42.20  
  Purchase #7 $88.43   12.149%   $99.1734   $99.17   $99.15   $99.20  
  7 purchase totals = $905.18       $996.0763   $996.08   $996.05   $996.10