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 $169.42   8.133%   $183.1989   $183.20   $183.20   $183.20  
  Purchase #2 $68.33   7.182%   $73.2375   $73.24   $73.25   $73.20  
  Purchase #3 $162.29   6.173%   $172.3082   $172.31   $172.30   $172.30  
  Purchase #4 $223.60   9.868%   $245.6648   $245.66   $245.65   $245.70  
  Purchase #5 $211.65   8.584%   $229.818   $229.82   $229.80   $229.80  
  Purchase #6 $236.63   9.475%   $259.0507   $259.05   $259.05   $259.10  
  Purchase #7 $56.72   11.653%   $63.3296   $63.33   $63.35   $63.30  
  7 purchase totals = $1,128.64       $1,226.6077   $1,226.61   $1,226.60   $1,226.60