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 $34.76   7.491%   $37.3639   $37.36   $37.35   $37.40  
  Purchase #2 $179.81   9.707%   $197.2642   $197.26   $197.25   $197.30  
  Purchase #3 $177.68   7.674%   $191.3152   $191.32   $191.30   $191.30  
  Purchase #4 $232.52   8.381%   $252.0075   $252.01   $252.00   $252.00  
  Purchase #5 $230.42   3.477%   $238.4317   $238.43   $238.45   $238.40  
  Purchase #6 $39.54   11.372%   $44.0365   $44.04   $44.05   $44.00  
  Purchase #7 $63.33   4.743%   $66.3337   $66.33   $66.35   $66.30  
  7 purchase totals = $958.06       $1,026.7527   $1,026.75   $1,026.75   $1,026.70