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 $127.38   5.122%   $133.9044   $133.90   $133.90   $133.90  
  Purchase #2 $199.26   10.185%   $219.5546   $219.55   $219.55   $219.60  
  Purchase #3 $135.52   9.490%   $148.3808   $148.38   $148.40   $148.40  
  Purchase #4 $158.88   11.177%   $176.638   $176.64   $176.65   $176.60  
  Purchase #5 $218.50   13.585%   $248.1832   $248.18   $248.20   $248.20  
  Purchase #6 $98.93   4.474%   $103.3561   $103.36   $103.35   $103.40  
  Purchase #7 $221.37   6.243%   $235.1901   $235.19   $235.20   $235.20  
  7 purchase totals = $1,159.84       $1,265.2072   $1,265.20   $1,265.25   $1,265.30