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 $179.52   11.442%   $200.0607   $200.06   $200.05   $200.10  
  Purchase #2 $237.43   12.385%   $266.8357   $266.84   $266.85   $266.80  
  Purchase #3 $234.74   13.825%   $267.1928   $267.19   $267.20   $267.20  
  Purchase #4 $122.27   11.167%   $135.9239   $135.92   $135.90   $135.90  
  Purchase #5 $158.56   4.397%   $165.5319   $165.53   $165.55   $165.50  
  Purchase #6 $231.91   13.178%   $262.4711   $262.47   $262.45   $262.50  
  Purchase #7 $38.86   10.748%   $43.0367   $43.04   $43.05   $43.00  
  7 purchase totals = $1,203.29       $1,341.0528   $1,341.05   $1,341.05   $1,341.00