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 $209.52   11.120%   $232.8186   $232.82   $232.80   $232.80  
  Purchase #2 $209.80   13.221%   $237.5377   $237.54   $237.55   $237.50  
  Purchase #3 $48.31   5.566%   $50.9989   $51.00   $51.00   $51.00  
  Purchase #4 $135.63   9.834%   $148.9679   $148.97   $148.95   $149.00  
  Purchase #5 $54.61   3.689%   $56.6246   $56.62   $56.60   $56.60  
  Purchase #6 $117.91   4.240%   $122.9094   $122.91   $122.90   $122.90  
  Purchase #7 $140.32   7.308%   $150.5746   $150.57   $150.55   $150.60  
  7 purchase totals = $916.10       $1,000.4317   $1,000.43   $1,000.35   $1,000.40