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 $202.86   8.460%   $220.022   $220.02   $220.00   $220.00  
  Purchase #2 $22.92   4.123%   $23.865   $23.87   $23.85   $23.90  
  Purchase #3 $177.89   11.176%   $197.771   $197.77   $197.75   $197.80  
  Purchase #4 $138.35   6.859%   $147.8394   $147.84   $147.85   $147.80  
  Purchase #5 $64.62   13.848%   $73.5686   $73.57   $73.55   $73.60  
  Purchase #6 $138.38   6.465%   $147.3263   $147.33   $147.35   $147.30  
  Purchase #7 $24.39   10.420%   $26.9314   $26.93   $26.95   $26.90  
  7 purchase totals = $769.41       $837.3237   $837.33   $837.30   $837.30