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 $181.54   12.793%   $204.7644   $204.76   $204.75   $204.80  
  Purchase #2 $178.55   4.745%   $187.0222   $187.02   $187.00   $187.00  
  Purchase #3 $143.45   6.356%   $152.5677   $152.57   $152.55   $152.60  
  Purchase #4 $11.27   6.501%   $12.0027   $12.00   $12.00   $12.00  
  Purchase #5 $176.25   9.215%   $192.4914   $192.49   $192.50   $192.50  
  Purchase #6 $179.86   8.283%   $194.7578   $194.76   $194.75   $194.80  
  Purchase #7 $194.31   4.339%   $202.7411   $202.74   $202.75   $202.70  
  7 purchase totals = $1,065.23       $1,146.3473   $1,146.34   $1,146.30   $1,146.40