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 $176.98   4.284%   $184.5618   $184.56   $184.55   $184.60  
  Purchase #2 $174.58   13.367%   $197.9161   $197.92   $197.90   $197.90  
  Purchase #3 $185.94   10.614%   $205.6757   $205.68   $205.70   $205.70  
  Purchase #4 $12.67   11.492%   $14.126   $14.13   $14.15   $14.10  
  Purchase #5 $203.61   7.479%   $218.838   $218.84   $218.85   $218.80  
  Purchase #6 $71.94   3.720%   $74.6162   $74.62   $74.60   $74.60  
  Purchase #7 $114.42   9.303%   $125.0645   $125.06   $125.05   $125.10  
  7 purchase totals = $940.14       $1,020.7983   $1,020.81   $1,020.80   $1,020.80