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 $134.38   11.380%   $149.6724   $149.67   $149.65   $149.70  
  Purchase #2 $145.89   7.829%   $157.3117   $157.31   $157.30   $157.30  
  Purchase #3 $119.82   4.228%   $124.886   $124.89   $124.90   $124.90  
  Purchase #4 $124.99   9.813%   $137.2553   $137.26   $137.25   $137.30  
  Purchase #5 $158.98   9.216%   $173.6316   $173.63   $173.65   $173.60  
  Purchase #6 $62.56   4.777%   $65.5485   $65.55   $65.55   $65.50  
  Purchase #7 $228.96   6.240%   $243.2471   $243.25   $243.25   $243.20  
  7 purchase totals = $975.58       $1,051.5526   $1,051.56   $1,051.55   $1,051.50