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 $55.53   13.152%   $62.8333   $62.83   $62.85   $62.80  
  Purchase #2 $245.41   11.205%   $272.9082   $272.91   $272.90   $272.90  
  Purchase #3 $208.94   7.210%   $224.0046   $224.00   $224.00   $224.00  
  Purchase #4 $142.84   5.272%   $150.3705   $150.37   $150.35   $150.40  
  Purchase #5 $202.91   11.392%   $226.0255   $226.03   $226.05   $226.00  
  Purchase #6 $222.39   5.714%   $235.0974   $235.10   $235.10   $235.10  
  Purchase #7 $95.60   11.762%   $106.8445   $106.84   $106.85   $106.80  
  7 purchase totals = $1,173.62       $1,278.0840   $1,278.08   $1,278.10   $1,278.00