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 $65.93   8.640%   $71.6264   $71.63   $71.65   $71.60  
  Purchase #2 $122.89   8.654%   $133.5249   $133.52   $133.50   $133.50  
  Purchase #3 $178.96   8.796%   $194.7013   $194.70   $194.70   $194.70  
  Purchase #4 $168.65   4.717%   $176.6052   $176.61   $176.60   $176.60  
  Purchase #5 $119.58   9.664%   $131.1362   $131.14   $131.15   $131.10  
  Purchase #6 $134.38   9.437%   $147.0614   $147.06   $147.05   $147.10  
  Purchase #7 $193.37   13.349%   $219.183   $219.18   $219.20   $219.20  
  7 purchase totals = $983.76       $1,073.8384   $1,073.84   $1,073.85   $1,073.80