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 $204.25   11.168%   $227.0606   $227.06   $227.05   $227.10  
  Purchase #2 $59.91   12.270%   $67.261   $67.26   $67.25   $67.30  
  Purchase #3 $156.91   5.691%   $165.8397   $165.84   $165.85   $165.80  
  Purchase #4 $62.88   4.573%   $65.7555   $65.76   $65.75   $65.80  
  Purchase #5 $157.48   12.151%   $176.6154   $176.62   $176.60   $176.60  
  Purchase #6 $205.93   13.391%   $233.5061   $233.51   $233.50   $233.50  
  Purchase #7 $206.40   11.462%   $230.0576   $230.06   $230.05   $230.10  
  7 purchase totals = $1,053.76       $1,166.0959   $1,166.11   $1,166.05   $1,166.20