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 $217.36   5.484%   $229.28   $229.28   $229.30   $229.30  
  Purchase #2 $119.78   4.313%   $124.9461   $124.95   $124.95   $124.90  
  Purchase #3 $202.38   5.784%   $214.0857   $214.09   $214.10   $214.10  
  Purchase #4 $79.25   7.822%   $85.4489   $85.45   $85.45   $85.40  
  Purchase #5 $169.76   4.809%   $177.9238   $177.92   $177.90   $177.90  
  Purchase #6 $14.56   10.410%   $16.0757   $16.08   $16.10   $16.10  
  Purchase #7 $170.89   7.722%   $184.0861   $184.09   $184.10   $184.10  
  7 purchase totals = $973.98       $1,031.8463   $1,031.86   $1,031.90   $1,031.80